Report on High Rise Building
In reinforced concrete buildings, slabs are used to provide flat, useful surfaces. A reinforced concrete slab is a broad, flat plate, usually horizontal, with top and bottom surfaces parallel or nearly so. The slabs are presented in two groups: one-way slabs and two-way slabs. When a rectangular slab is supported on all the sides and the length-to-breadth ratio is less than two, it is considered to be a twoway slab. The slab spans in both the orthogonal directions. A circular slab is a two-way slab. In general, a slab which is not falling in the category of one-way slab is considered to be a two-way slab. Rectangular two-way slabs can be divided into the following types. 1) Flat plates: These slabs do not have beams between the columns, drop panels or column capitals. Usually, there are spandrel beams at the edges. 2) Flat slabs: These slabs do not have beams but have drop panels or column capitals. 3) Two-way slabs with beams: There are beams between the columns. If the beams are wide and shallow, they are termed as band beams. For long span construction, there are ribs in both the spanning directions of the slab. This type of slabs is called waffle slabs.
The slabs can be cast-in-situ (cast-in-place). Else, the slabs can be precast at ground level and lifted to the final height. The later type of slabs is called lift slabs. A slab in a framed building can be a twoway slab depending upon its length-to-breadth (L / B) ratio. Two-way slabs are also present as mat (raft) foundation. The following sketches show the plan of various cases of two-way floors or roofs. The spanning directions in each case are shown by the double headed arrows:-
Figure 1.1 Plans of two-way floor/roof system So the Flat Slab and Flat Plate is the reinforced concrete floor/roof system supported directly by concrete columns without the use of beams and girders. Generally, the slab may be of uniform thickness throughout the entire floor area, or a part of it, symmetrical about the column, may be made somewhat thicker than the rest of the slab, the thickened portion of the slab thus formed constituting what is known as a dropped panel, or drop. Dropped panels are used to reduce the shearing stress in the slab thickness provided by the drop also decreases the compression stresses in the concrete and reduces the amount of steel which required over the column heads. Flat Slabs and Flat Plates may be supported on two opposite side columns only, in which case the structural action of the slab is essentially one-way, the loads being carried by the floor in the direction perpendicular to the supports. On the other hand, there may be supports on all four sides, so that twoway action is obtained. If the ratio of length to width of one floor panel is larger than about 2, most of the load is carried in the short direction. As per ACI 318-02 (Building Code Requirements for Structural Concrete, American Concrete Institute, this building code is almost equivalent to BNBC), the limits of span-to-depth ratios are as follows:For floors 42 For roofs 48.
The values can be increased to 48 and 52, respectively, if the deflection, camber and vibration are not objectionable. The following photographs show flat plate and flat slab:-
(a) Flat plate (b) Flat slab Figure 1.2 Two-way Flat Floors (Courtesy: VSL India Pvt. Ltd.) However, due to their economy and speed of construction, flat floors are very common structural elements for apartments, office and institutional buildings etc. It is well established that, the capacity of flat floors is often governed by shear capacity in the vicinity of the columns. In general for the analysis purpose, the building structures are analyzed using a model structure of that entire building with the philosophy of analysis prescribed in different existing methods of structural engineering. For easy understanding and suitable execution of structural behavior of any structure, the 2-D modeling & analysis is generally done in nature. 2-D models are prepared based on the different planes of structures. In case of 2-D model, one may consider any existing plan or elevation of an entire structure to calculate the intended values. Here the process to calculate desired values for any individual section of the entire structure is also possible. As in 2-D model only the skeletal diagram and imposed loads of the entire structure is considered, thus it is suitable to analyze and to consider for any further action to be implemented. But it is more recommended to analyze a structure by considering its 3-D model with its all compatibility from the view point of precision or accuracy of intended values to determine structural behavior, though the analysis procedures considering 3-D model are always be considered as complex task. However, with invent of digital computer based programs using complex structural philosophy made it a process of ease and comfort for the structural engineers. A digital computer based program named STAAD Pro is referable. Where, STAAD.Pro is the most popular structural engineering software product for 3D model generation, analysis and multi-material
design. It has an intuitive, user-friendly GUI, visualization tools, powerful analysis and design facilities and seamless integration to several other modeling and design software products. For static or dynamic analysis of bridges, containment structures, embedded structures (tunnels and culverts), pipe racks, steel, concrete, aluminum or timber buildings, transmission towers, stadiums or any other simple or complex structure, STAAD.Pro has been the choice of design professionals around the world for their specific analysis needs. Another program named ABAQUS is also referable for computing deflection of beams. ABAQUS is a powerful finite element software package. It is used in many different engineering fields throughout the world. ABAQUS performs static and/or dynamic analysis and simulation on structures. It can deal with bodies with various loads, temperatures, contacts, impacts, and other environmental conditions. 1.2 Objectives and Scopes of the Study Now-a-days, in case of high-rise building construction the flat floor is a common practice. Thus, due to importance of flat plate floor analysis to have from various points of view, our thesis and project work is operated for achieving the following purposes and scopes:-
1. To analyze a flat slab using software STAAD Pro considering its 2-D model. 2. To analyze a flat slab using software STAAD Pro considering its 3-D model. 3. Comparing results of analysis obtained from 2-D & 3-D model, and also to compare the axial force got using Equivalent Frame Method by hand calculation to with the axial force got in the analysis done by software STAAD Pro. 4. Checking the change in the behavior when a structure is modeled 2-D and 3-D both using software STAAD Pro. 5. General idea and Small briefing about the common methods to analyze & design a flat floor. 6. Software compatibility and proper basis of 2-D & 3-D modeling of a high-rise building. 7. Representing results properly in tables and plotting them into graphs. 8. Preparing hand calculation for design and analysis purpose in case of flat floors.
This report also includes the following purposes as additional attachments:•
General modeling and analysis of a beam using software ABAQUS.
Comparison of deflection of that beam by the construction of graph based on the analysis output of ABAQUS
Review of Literature
2.1 Background The flat plate system, in which columns directly support floor slabs without beams, is adopted for many building structures recently constructed. However, the following considering topics will clarify the idea about flat slab in general case: •
It is the simplest and most logical of all structural forms in that it consists of uniforms slabs, connected rigidly to supporting columns.
The system, which is essentially of reinforced concrete, is very economical in having a flat soffit requiring the most uncomplicated formwork and, because of the soffit can be used as the ceiling, in creating a minimum possible floor depth.
Lateral resistance depends on the flexural stiffness of the components and their connections, with the slab corresponding to the girder of the rigid frame.
Particularly appropriate for hotel and apartment construction where ceiling space is not required and where the slab may serve directly as the ceiling.
Since flat plate system was primarily developed to resist the gravity loads, many researches on the resistance capacity for lateral loads have been undertaken. In the analysis of a flat plate structure subjected to gravity loads, direct design method or equivalent frame method is generally used for the rectangular type slabs. However, we have already informed that flat floors/roofs are generally of two type are•
Flat Slabs with dropped panel (Flat Slab)
Flat Slabs without dropped panel (Flat Plate)
Characterization of Flat Slabs due to their existing components, Flat Slabs may also be characterized in other two more categories areâ€˘
Flat slab with column head panels
Flat slab with drop panel and column head
Figure 2.1 General Types of Flat Structures 2.2 Technical Terms of Flat Structures 2.2.1 Dropped Panel / Drop A part of the flat slab that is symmetrical about the column may be made somewhat thicker than the rest of the slab is termed as dropped panel or drop.
Uses of drop panels: •increase shear strength of slab •increase negative moment capacity of slab •stiffen the slab and hence reduce deflection
Figure 2.2.1 Drop Panel 2.2.2 Column Head / Column Capital The column in practically all cases flare out toward the top, forming a capital of a shape somewhat similar to an inverted truncated cone, is termed as Column Head or Column Capital. Uses of Column Capital:
increase shear strength of slab
reduce the moment in the slab by reducing the clear or effective span
Figure 2.2.2 Column Head
2.2.3 Analysis Strip Generally the slab panel is divided into strips according to their existing line as per the requirement of specification of standard codes, these strips are known as analysis Strip.In general, the prospective analysis strip is subdivided into the following identical strip region are1. Column Strip
A column strip is defined as a strip of slab having a width of each side of the column centre line as per specification of any standard codes for practice.
2. Middle Strip A middle strip is a design strip bounded by two column strips.
Figure 2.2.3 (a) Strip with no drop. 2.3
Figure 2.2.3 (b) Strip with drop
Advantages of Flat Slab/Flat Plate Floor
Flexibility in Room Layout •
allows Architect to introduce partition walls anywhere required
allows owner to change the size of room layout
allows choice of omitting false ceiling and finish soffit of slab with skim coating
Saving Building Height •
Lower storey height will reduce building weight due to lower partitions and cladding to façade
approx. saves 10% in vertical members
reduce foundation load
Figure 2.3.2 Saving Building Height
Shorter Construction Time â€˘
flat plate design will facilitate the use of big table formwork to increase productivity
Figure 2.3.3 Big Table Formwork
Single Soffit Level •
Simplified the table formwork needed
Figure 2.3.4 Single Soffit Level
Ease of Installation of M & E services •
all M & E services can be mounted directly on the underside of the slab instead of bending them to avoid the beams
avoids hacking through beams
Pre-Fabricated Welded Mesh •
Prefabricated in standard sizes
Minimized installation time
Better quality control
Figure 2.3.6 Pre-Fabricated Welded Mesh
Buildable Score •
allows standardized structural members and prefabricated sections to be integrated into the design for ease of construction
this process will make the structure more buildable, reduce the number of site workers and increase the productivity at site
more tendency to achieve a higher Buildable score
Structural Behavior of Flat Structures
The Flat Slabs/Plates discussed deform under load into an approximately cylindrical surface. The main structural action is on way in such cases, in the direction normal to supports on two- way opposite edges of a rectangular panel. In many cases, however, rectangular slabs are of
proportions and are supported in such a way that two- way action results .When loaded , such slabs bend into a dished surface rather than a cylindrical one. This mean that at any point of the slab is curved in both principle directions, and since bending moments are proportional to curvatures, moments also exist in both directions. To resist these moments, the slab must be reinforced in both directions, by at list two layers of bars perpendicular, respectively, to two pairs of edges. The slab must be designed to take a proportionate share of load in each direction .In general, One sees that the large share of load is carried in the short direction, the ratio of the two portions of the total load being inversely proportional to the 4th power of the ratio of the spans of the considering slab. This assumption is approximate because the actual behavior of slab is more complex.
Consistent with the assumptions of the analysis of two-way edge supported slabs; the main flexure reinforcement is placed in an orthogonal pattern, which reinforcing bars parallel and perpendicular to the supported edge. As the positive steel is placed in two layers, the effective depth for the upper layer is smaller than that for the lower layer by one bar diameter. Because the moments in the long direction are the smaller one, it is economical to place the steel in that direction on top of the bars in the short direction. The stacking
problem doesnâ€™t exist for negative reinforcement perpendicular to the
supports except at the corner. Either straight bars, cut-off where they are no longer required or bent bars may be used for two way slabs, but economy of bar fabrication and placement will generally favor on straight bars. The precise locations of inflection point arenâ€™t easily determined, because they depend upon the side ratio, the ratio of live to dead load, and continuity conditions at the edges.
In case of flat slabs, if a surface load w is applied, that load is shared between imaginary slab strips l a in the short direction and lb in the long direction, as described in the previous lines in this section.
la= Length in short direction lb= Length in Long direction
The portion of the load that is carried by the long strips l b is delivered to the beams B1 spanning in the short direction of the panel. The portion carried directly by the in the short direction by the slab strips la, sums up to 100 percent of the load applied to the panel. Similarly, the short-direction slab strips l a deliver a part of the load to long direction. That load, plus the load carried directly in the long by the slab, includes 100 percent of the applied load. It is clearly a requirement of statics that, for columnsupported construction, 100 percent of the applied load must be carried in each direction, jointly by the slab and its supporting columns. However, it is interesting to compare the behavior of flat plate with that of two-way slabs in flat plate analysis; the full load is assumed to be carried by the slab in each of the two perpendicular directions. This is in apparent contrast to the analysis of two-way slabs, in which the load is divided, one part carried by the slabs in the short direction, and the remainder carried by the slabs in the long direction. However, in two-way slabs, while only a part of the loads is carried by the slabs in the short direction, the remainder is transmitted in the perpendicular direction to marginal beams, which then also span in the short direction. Similarly, which part of the load carried by the slab in long direction, the remainder is transmitted by the slab in the short direction to marginal beams which span is long
direction. It is evident that in two-way slabs, as in flat slabs, conditions of equilibrium required that the entire load be carried in each of the two-way principal directions. 2.5
Wall and Column Position •
Locate position of wall to maximize the structural stiffness for lateral loads.
Facilitates the rigidity to be located to the centre of building.
Optimization of Structural Layout Plan •
The sizes of vertical and structural structural members can be optimized to keep the volume of concrete for the entire superstructure inclusive of walls and lift cores to be in the region of 0.4 to 0.5 m3 per square meters.
Deflection Check •
Necessary to include checking of the slab deflection for all load cases both for short and long term basis.
In general, under full service load, δ< L/250 or 40 mm whichever is smaller.
Limit set to prevent unsightly occurrence of cracks on nonstructural walls and floor finishes.
Crack Control •
Advisable to perform crack width calculations based on spacing of reinforcement as detailed and the moment envelope obtained from structural analysis.
Good detailing of reinforcement will–restrict the crack width to within acceptable tolerances as specified in the codes and –reduce future maintenance cost of the building
Floor Openings •
No opening should encroach upon a column head or drop.
Sufficient reinforcement must be provided to take care of stress concentration.
Punching Shear •
Always a critical consideration in flat plate design around the columns.
Instead of using thicker section, shear reinforcement in the form of shear heads, shear studs or stirrup cages may be embedded in the slab to enhance shear capacity at the edges of walls and columns.
Figure 2.5.6 Shear Condition 2.5.7
Construction Loads •
Critical for fast track project where removal of forms at early strength is required.
Possible to achieve 70% of specified concrete cube strength within a day or two by using high strength concrete.
Alternatively use 2 sets of forms.
Lateral Stability •
Buildings with flat plate design are generally less rigid.
Lateral stiffness depends largely on the configuration of lift core position, layout of walls and columns.
Frame action is normally insufficient to resist lateral loads in high rise buildings, it needs to act in tendam with walls and lift cores to achieve the required stiffness.
MULTIPLE FUNCTION PERIMETER BEAMS -lateral rigidity -reduce slab deflection.
Design Methodology The study presented here is concerned with the investigation of methods for determining moments in reinforced concrete slabs by the analysis of equivalent two-dimensional elastic frames and by the philosophy of approximate method in association with analysis software. Thus, the study is based on the quantitative comparison of moments in slabs as determined from analysis.
Common Methods of Design •
The finite element method.
The simplified method or, direct design method.
The equivalent frame method or cantilever method.
Finite Element Method •
Based upon the division of complicated structures into smaller and simpler pieces (elements) whose behavior can be formulated.
E.g., of software includes STAAD PRO, ETABS, SAFE, ADAPT, etc.
Results includes–moment and Shear Envelopes –contour of structural deformation
Simplified or Direct Design Method 22.214.171.124 Basis of Analysis Moments in two-way slabs can be found using the semi empirical direct design method, subject to the following restrictions: 1. There must be a minimum of three continuous spans in each direction. 2. The panels must be rectangular, with the ratio of the longer to the shorter spans within a panel not greater than two. 3. The successive span lengths in each direction must not differ by
than one-third of the longer span. 4. Columns may be offset a maximum of 10 percent of the span in the direction of the offset from either axis between centerlines of successive columns. 5. Loads must be due to gravity only and the live load must not exceed two times the dead load. 6. If beams are used on the column lines, the relative stiffness of the beams in the two perpendicular directions, given by the ratio α 1 l2 2 / α2 l1 2 must be between 0.2 and 5.0
Total Static Moment at Factored Loads
For purposes of calculating the total static moment M o in a panel, the clear span l n in the direction of moments is used. The clear span is defined to extend from face to face of the columns, capitals, brackets, or walls but is not to be less than 0.65 l 1 The total factored moment in a span, for a strip bounded laterally by the centerline of the panel on each side of the centerline of supports, is Mu = wul2ln2 / 8
Assignment of Moments to Critical Sections
For interior spans, the total static moment is apportioned between the critical positive and negative bending sections according to the following ratios: Negative factored moment: Neg Mu = 0.65 Mo Positive factored moment: Pos Mu = 035 Mo The critical section for negative bending is taken at the face of rectangular supports, or at the face of an equivalent square support having the same cross-sectional area as a round support.
Figure 126.96.36.199(A) Distribution of total static moment M0 to critical sections for positive and negative bending.
Figure 188.8.131.52(B) Conditions of edge restraint considered in distributing total static moment Mo to critical sections in an end span: (a) exterior edge unrestrained, e.g., supported by a masonry wall; (b) slab with beams between all supports; (c) slab without beams, i.e., flat plate; (d) slab without beams between interior supports but with edge beam; (e) exterior edge fully restrained, e.g., by monolithic concrete wall.
The Equivalent Frame Method 184.108.40.206 Basis of Analysis The equivalent frame method is recommended by ACI 318-02 (ACI code is almost equivalent to BNBC). It is given in Subsection 31.5, IS:456 - 2000. This method is briefly covered in this section for flat plates and flat slabs.
The slab system is represented by a series of two dimensional equivalent frames for each spanning direction. An equivalent frame along a column line is a slice of the building bound by the centre-lines of the bays adjacent to the column line. The width of the equivalent frame is divided into a column strip and two middle strips. The column strip (CS) is the central half of the equivalent frame. Each middle strip (MS) consists of the remaining portions of two adjacent equivalent frames. The following figure shows the division in to strips along one direction. The direction under investigation is shown by the double headed arrow in the figure given below:-
Figure 220.127.116.11(a) Equivalent frame along Column Line 2
The analysis is done for each typical equivalent frame. An equivalent frame is modeled by slab-beam members and equivalent columns. The equivalent frame is analyzed for gravity load and lateral load (if required), by computer or simplified hand calculations. Next, the negative and positive moments at the critical sections of the slab-beam members are distributed along the transverse direction. This provides the design moments per unit width of a slab. If the analysis is restricted to gravity loads, each floor of the equivalent frame can be analyzed separately with the columns assumed to be fixed at their remote ends, as shown in the following figure. The pattern loading is applied to calculate the moments for the critical load cases.
Figure 18.104.22.168(b) Simplified model of an equivalent frame 22.214.171.124 The Equivalent Column In the equivalent frame method of analysis, the columns are considered to be attached to the continuous slab beam by torsional members that are transverse to the direction of the span for which moments are being found; the torsional member extends to the panel centerlines bounding each side of the slab beam under study. Torsional deformation of these transverse supporting members reduces the effective flexural stiffness provided by the actual column at the support. This effect is accounted for in the analysis by use of what is termed an equivalent column having stiffness less than that of the actual column. To allow for this effect, the actual column and beam are replaced by an equivalent column, so defined that the total flexibility (inverse of stiffness) of the equivalent column is the sum of the flexibilities of the actual column and beam. Thus, 1 /Kec = 1 /âˆ‘Kc + 1 /âˆ‘Kt Where, Kec = flexural stiffness of equivalent column Kc = flexural stiffness of actual column Kt = torsional stiffness of edge beam The effective cross section of the transverse torsional member, which may or may not include a beam web projecting below the slab, as shown in Fig. 13.18, is the
Figure 126.96.36.199(a) Torsion at a transverse supporting member illustrating the basis of the equivalent column.
Steps–by-Step Analysis Procedures of Equivalent Frame Method
The steps of analysis of a two-way slab are as follows:1) Determine the factored negative (Mu–) and positive moment (Mu+) demands at the critical sections in a slab-beam member from the analysis of an equivalent frame. The values of Mu– are calculated at the faces of the columns. The values of Mu+ are calculated at the spans. The following sketch shows a typical moment diagram in a level of an equivalent frame due to gravity loads.
Figure 188.8.131.52(b) Typical moment diagram due to gravity loads 2) Distribute Mu– to the CS and the MS. These components are represented as Mu,– CS and Mu,–MS, respectively. Distribute Mu+ to the CS and the MS. These components are represented as Mu,+CS and Mu,+MS, respectively.
Figure 184.108.40.206(c) Distribution of moments to column strip and middle strips
3) If there is a beam in the column line in the spanning direction, distribute each of Mu,CS and Mu,+CS between the beam and rest of the CS.
Figure 220.127.116.11(d) Distribution of moments to beam, column strip and middle strips 4) Add the moments Mu,–MS and Mu,+MS for the two portions of the MS (from adjacent equivalent frames). 5) Calculate the design moments per unit width of the CS and MS.
2.6.5 Provision of Thickness According to ACI Code for the design and analysis of flat structures In order to prevent undue deflection, certain limitations are placed on the minimum slab thickness that can be used in a given floor panel. In as much as the actual deflection of a flat slab cannot be computed with any appreciable degree of accuracy, these limitations were developed from a study of the observed deflections in actual structures. The ACI code specifies that the slab thickness, exclusive of the drop, shall not be less than 1/40 of the longer dimension for slabs with drops, and not less than 1/36 of the same dimension for slabs without drops. Of course, the slab must also be thick enough so that allowable unit compressive and shear stresses will not exceed. In this connection, the ACI Code requires that a reduced effective width be used in calculating flexural compression stress, in order to allow for the non-uniform variation of bending moment across the width of the critical sections. This reduced effective width is to be taken as ¾
the width of the strip, except that on a section through a
drop panel ¾ th the width of the drop panel is to be used.
Previous Works on Related Topic
Recent time it is a common practice that of flat slab analysis, design and construction, and its importance is increasing with time in our country. As the gradual increasing of use and construction of flat slab, the researches related to flat slab is also gradually increased. Thus why, here we have represent gist of some previous thesis as an additional compliment for the viewers, and as a completion of our project work.
Gist of Previous Work
Researchers of Ahsanullah University of Science & Technology (AUST) did various thesis on different relevant subject of structures. The senior students have chosen different fields of study with the requirement of their time. The gist of their study reports are represented below:
Value engineering of mat foundation of the campus of Ahsanullah University of Science & Technology by Md. Mahmudul Hasan, Swim Iqbal Munna, A.K.M Sydat and Mosaharof Hoshain Sumon (on Seeptember 2004) under the supervision of Professor Dr. Anwarul Mustafa (P.Engg). In this thesis all the design criteria of AUST Campus is checked including mat foundation analytically and value engineering of the project. They recommended mat foundation in the case of heavy load and for weak soil strata with much variation in water level. They also mentioned various processes for mat foundation and they are finite difference method.
Design of prestress concrete girder bridge by Syed Asadul Haque and Md. Rezaul Islum (on November 2002) under the supervision of Professor Dr. Anwarul Mustafa (P.Engg). In this thesis they want to establish a comparative study of different methods loading analysis of bridge girder and the analytic value of bending moment, shear force, torsion are greater than the amount found by grid analysis. So the economic and more reliable method of prestress concrete girder bridge is the main aspects of this thesis.
Design of steel truss bridge by Ziaul Haque Ali and A.K.M Hasan-Al-Farouque (on November 20002) under the supervision of Professor Dr. Anwarul Mustafa (P.Engg). In this thesis long span highway steel truss bridge is analyzed. Their recommendation of this bridge is economical for a range of 100m-200m; facility is easy to establish due to lightness of this structure nad fabrication of joints at site. But maintenance cost is quite expensive. So the value engineering is necessary in this case, they recommended.
Computer aided analysis and design of fifteen storied apartment building in addition to approximate method by S.M Arif Reza Hossain, Farjana Haque, Md. Ashraf Uzzaman and Syed Mosiur Rahman (session 2000) under the supervision of Dr. Md. Mahmudur Rahman, Associate Professor, AUST. In this thesis they designed & analyzed the static and dynamic load of fifteen storied apartment building based on various analysis software, for example, STAAD Ш, GT STRUDL etc. They also compare the difference of result between ACI Co-
efficient Method and Software. A full soil integrated analysis of their project was the future recommendation.
Design of a 20 Storied Flat Plate Building by A.T.M Nurujjaman Khan (session 2000-2001) under the supervision of Professor Dr. Al-Hajj Kazi Harun-Ur-Rashid, AUST and the Director of Shaheedullah and new Associates Ltd. In this thesis paper they design a flat plate, and also analyze, using various method of design and analysis. The use of Portal Frame Method for analyzing frames. The important thing of their thesis outcome is that, flat plate creates in high-rise building construction by reducing frame work’s cost. Reduction of Story Height resulting from thin floor, the smooth ceiling and possibility of slightly shifting column location to fit the room arrangements, and all their approaches are for achieving economy and thus creating flexibility of architectural arrangement.
Investigation on Effective bracing System for Buildings with Soft Ground Story Under Seismic loading by Md. Nazmul Islum, Md. Ziaul Badr and Md. Abdullah Al Mamun (on October 2008) under the supervision of Dr. Md. Mahmudur Rahman, Associate Professor, AUST. In this thesis, they aims at proposing an effective bracing system in the open ground story to mitigate large deflection and lessen force demand. For this why, five different cases of bracing system for a typical six storied building are analyzed. The three dimensional (3-D) reinforced concrete frames are modeled by finite element software, ETABS, under design load following Bangladesh National Building Code (BNBC). Frames are then analyzed under lateral earthquake load provide by ETABS following UBC 94, which shows equivalent result with BNBC. Then, story displacement and force demand (Moment and Shear) for the system is compared with those from open story system (Braced Frame).
Structural Analysis of the Flat Plate of a 20 Storied Building Using Structural Software STAAD Pro-2004 by Mukarram Mahmud Sohul and Md. Shariful Hasan Khan under the supervision of Dr. Md. Mahmudur Rahman, Associate Professor, Ahsanullah University of Science & Technology. In that thesis, the structural analysis of flat plate for a 20 storied building was done with the help of structural analysis software named STAAD Pro-2004. They analyzed deflection, bending moments and the shear forces of the structural frame for various sections such as, interior column strip, interior middle strip, end span column strip, end span middle strip etc. They have also compared the software results of the bending
moment and shear forces of flat plate of the mode at various critical sections, with the results they got from analytical approximate calculation. 03. Modeling and Analysis
3.1 General of Modeling Modeling of most common type components such as slabs, beams, columns, etc. do not require any special techniques. However there are certain issues that need to be take care. In order to analyze the center row of panels, it is assumed that the structure is divided into five rows of panels in the direction of analysis. The boundaries of the center strip are assumed to be the centerlines of the interior rows of columns. This strip is dimensionally identical to a strip containing an interior row of columns and bounded by the panel centerline so for simplicity, the illustrations show the entire column at the center of the panel rather than half of it at each side. Flat slab floors are ordinarily designed to carry only uniform load over the entire surface. Important of those will be introduced in the following paragraphs: 3.1.1 Slabs: The important considerations in modeling slabs are what type of elements to be used, what should be the connectivity condition between slab and beam; and how to transfer the load from slab to other members. Precast panels with topping are modeled as one way panels. In this case, there is no need to divide the panel into smaller elements. The floor loads can be applied directly on the panels which are transferred to the supporting beams/columns automatically. These panels are membrane type elements. Two way type load transfer behavior need to be captured, the slab can be modeled as membrane or plate type elements. If modeled as membrane, the load is transferred to the supporting members automatically and there is no need to divide the slab into smaller elements. In this case there will be no interaction between the slab and supporting elements. However the slab can also be modeled as Plate/Shell elements. 3.1.2 Columns: Columns are relative easier to model but relative difficult to design if they are too slender. As long as the columns are short columns, automated design features are generally reliable. However when the column becomes long column and subjected to more than one action, a comprehensive design procedure need to be used. In this case, the software estimated factors to compute the effective length factors, moment magnification parameters, sway/non-sway checks, minimum eccentricity calculations, etc. which have direct impact on direct (capacity, reinforcement) need to be carefully
examined and verified before accepting the program recommended reinforcement. It is quite common that program overestimates the moment magnification factor (5-10) for commonly used column sections in houses (20-30 x 20-30 cm and 3 m height) and computes the longitudinal bars based on excessively magnified moments. Therefore it is extremely important to understand the influence of different parameters in the design of long columns (especially the connectivity condition) and also to verify whether the automatically calculated values are reasonable or not.
3.2 Assumptions of Modeling The assumption being that no breaks in the continuity will be maintained in case of modeling of the entire flat slab surface. Broad strips of the slab centered on the column lines in each direction serve the same function as the beams; for this case, also, the full load must be carried in each direction. Here the considerable “Analysis Strips” have chosen according to BNBC code for approximate direct design method by hand calculation. For 2-D modeling in analysis software we have also used all but similar philosophy. There we have provided a rectangular width as a supplement of real beams through the column lines as same as of considering strip width calculated according to the philosophy of direct design method for achieving the condition of flat slab. According to BNBC the analysis strip width is 8 / (eight feet) in here. Existing columns are modeled as beam elements having same as property (height, material, cross section etc.) for actual column on the considering structural system. However, in STAAD Pro has some form of automatic constraint system being applied to represent the rigid region for the columnslab connection in the 2-D model. In case of 3-D model all the components are modeled conventionally similar to the actual structural philosophy. Here we have provided automated plate which is similar to actual property of the considering flat plate. We have also meshed the plate elements in a proportion of four by four (4 × 4 = 16) for the intended plates and two by two (2 × 2 = 4) for the other plates to get more précised results. Columns are modeled as beam elements having same as property (height, material, cross section etc.) for actual column on the considering structural system. Here all the ends of the columns are supported as fixed support.
However, as a whole the above assumption philosophy will be integrated with the followings:1. The panel is one of an infinite array of identical panels. 2. All panels are uniformly loaded. 3. The shear is uniformly distributed around the perimeter of the column capital. 4. The bars are weightless and undeformable. 5. The mass of the plate and the external loads are concentrated at the fixed supports. 6· The resultants of the direct stresses are bending moments acting at the fixed supports and at the ends of each bar. 7. The resultant of vertical shearing stresses are shearing forces acting at the fixed supports and at the ends of each bar.
3.3 Model Data Floor Area
: 76 /×48 / (3648 Sq. ft)
Panel Size/Plate Size
: 16 / ×19 /
Column to Column C/C distance in long direction
: 19 /
Column to Column C/C distance in short direction
: 16 /
Rectangular width of considering strip/ Size of the beams
: 8 / along the direction of analysis for interior panels and 4 / for exterior panels according to BNBC for 2-D model
Thickness of the rectangular width / slab/plate Height of the columns
: .625 / (7.5 // ) : 12 / for ground floor & 10 / for upper floors for both 2-D & 3-D model
Size of the columns
: 18// × 18// for both 2-D
and 3-D model
Restraints / Supports Condition
: Conventional Fixed Support for both 2-D & 3D model
: Automated material constants being in the analysis software (STAAD Pro) for both model
3.4 Model The below plan is the identical layout plan for the entire structure in case of modeling and analysis:-
Figure 18.104.22.168 2-D Skeletal Model View with Panel ID
Figure 22.214.171.124 2-D Rendered Model View
Figure 126.96.36.199 2-D Skeletal Model View with Member Load
Figure 188.8.131.52 3-D Skeletal Model View with Panel ID
Figure 184.108.40.206 3-D Model with Full Sections & Columns with Panel ID
Figure 220.127.116.11 3-D Rendered Model View
Figure 18.104.22.168 3-D Model Top View with Plate ID (Roof)
Figure 22.214.171.124 3-D Model Full View with Plate ID
Figure 126.96.36.199 3-D Model Top View with Node ID (Roof)
Figure 188.8.131.52 3-D Full Model View with Node ID
3.5 Generals of Analysis Flat slab floors are ordinarily designed to carry only uniform load over the entire surface. However, for analysis purpose, concentrated loads are to be sustained in addition to the uniform load; this will be introduced as nodal loads in the entire direction. Generally the self weight is categorized as dead load and uniform service live loads are introduced as plate loads for 3-D model and as member loads for 2-D model in case of analysis by using the analysis software STAAD Pro. One necessary consideration is that, where major openings in the slab occur, they should be framed by the slab itself or by additional beams to have the effect of restoring continuity of slab. This slab or beams should be analyzed properly so that the portion will be given sufficient strength to carry the entire floor load or concentrated load to be placed there. However, we didnâ€™t need that because we have neglected this condition here. Finally, all the applied loads are combined to get proper idealization and best comparison of outputs. 3.5.1
Load Data: Self Weight of the Structure
: To be calculated automatically by the software.
Service Live Load
: 100 psf (100 lb per sq. ft.)as plate load in 3-D model and 800 lb/ft (100psf Ă— 8 ft = 800 lb/ft) as member load in 2-D model.
Load input unit Load combination
: lb-ft (Pound-Feet) : Combination-1=SW+WL
Material Constants: Automated material constants are used, those are being in the analysis software (STAAD Pro) as default value in this case.
Analysis Condition Representation:
Figure 3.5.2(a) 3-D Pre-Processing for analysis
Figure 3.5.2(b) 3-D During analysis
Figure 3.5.2(c) 2-D Pre-Processing for analysis
Figure 3.5.2(d) 2-D During analysis
04. Results and Comparison 4.1 General Here we have made comparison tables and provide some necessary figures, which are representing the deviations and similarities between results got from “3-D and 2D Model” analysis is done using the analysis software named “STAAD PRO v8.0i”, and between results got from Equivalent Frame Method (i.e., we also consider the axial force got by analysis software in comparison to with axial force got by analytical hand calculation done based on Equivalent Frame Method). This table is made because also to see the change in moment when a structural plan turned into 3D Model from 2-D Model with its all compatibility. This table is a great scope to view and to consider the structure’s conduct variation from the view point of “Mechanism of Analysis” of any structure. We also represent the values of beam deflection got from ABAQUS and thus concurrently it is represented in a comparable graph. 4.2 Assumption For developing an idealization to get most clarified imagination about the whole structure’s behavior variation; specially in case of a high rise building, here we only consider the “Plate-Node Moments” which have been got using analysis software “STAAD PRO v8.0i”.Where the plates are positioned through the whole slabs and then meshed in case of 3-D modeling, and also there we have taken the beam width as same of “Analysis Strip” width of 8(eight) feet chosen according to BNBC code as per our honorable Project Supervisor’s guidance incase of 2-D modeling. Finally, we have tried to compare results through the column line of panel C-C for different floors as a whole. 4.3 Pictures Showing Diagrammatic Representation of Results Following represented pictures are needed to understand, and for the proper illustration of various comparisons those will be done next:-
Figure 4.3 (a) Showing 2-D full model with considering columns
Figure 4.3 (b) Considering columns of 2-D model with Beam ID
Figure 4.3 (c) Considering columns of 2-D model with Nodal ID
Figure 4.3 (d) Considering full 2-D model with Nodal ID (Scale 1:1)
Figure 4.3 (e) Shear FZ of 2-D model
Figure 4.3 (f) A.F FX of 2-D model
(Scale 1:550 lb per ft)
(Scale 1:10000 lb per ft)
Figure 4.3 (g) Deflected view of 2-D model (Scale 1: 0.2 in per ft)
Figure 4.3 (h) Moment MZ of 2-D model (Scale 1: 150 Kip-in per ft)
Figure 4.3 (i) Moment MY of 2-D model (Scale 1: 50 Kip- in per ft)
Figure 4.3 (j) 3-D skeletal model with considering column positioned in panel C-C (Scale 1:1)
Figure 4.3 (k) Considering columns of 3-D model Figure 4.3 (l) Considering columns of with Nodal ID
Figure 4.3 (m) Shear FZ of 3-D model (Scale 1: 400 Kip-in per ft)
3-D model with Beam ID
Figure 4.3 (n) A.F FX of 3-D model (Scale 1: 10000 Kip-in per ft)
Figure 4.3 (o) 1st Floor of 3-D model with plate ID
Figure 4.3 (p) 1st Floor of 3-D model with nodal ID
Figure 4.3 (q) 5th Floor of 3-D model with plate ID
Figure 4.3 (r) 5th Floor of 3-D model with nodal ID
Figure 4.3 (s) Deflected view of 3-D model (Scale 1: 0.2 in per ft)
Figure 4.3 (t) Moment MZ of 3-D model for columns (Scale 1: 30 Kip-in per ft)
Figure 4.3 (u) Moment MY of 3-D model for columns (Scale 1: 60 Kip-in per ft)
Comparison Tables & Graphs
The below tables & graphs are prepared for understanding of deviation of results and thus, variations in structureâ€™s behavior under different condition at different considerable positions. The graphs are made with the help of Microsoft Excel, where automated graph can be got according to selected input data For comparison of nodal moments of 3-D model between story one and five, it is important to note that, here the moment for plate corner stress is considered and thus moments for the plates around a node are sum-up in case of their negative and positive values of moments of the surrounding plates
Plate Node Moment Type
Table 4.1 Plate Node Moment (-ve & +ve): 3-D vs 3-D of different story 3-D Model 3-D Model
1 st Floor, Panel C-C
R E M A R K S
5 th Floor, Panel C-C
Load Case: Combination-1
Load Case: Combination-1
Moment in kip-ft/ft
Moment in kip-ft/ft
Same Localized Nodes
(Through Panel C-C)
(Through Panel C-C)
Note: GL = Grid Line
The moment values have similarity & dissimilarity both.
Same Localized Nodes
Table 4.2 Column Shear (-ve & +ve): 2-D vs 3-D Model
Exterior Column in C-C Panel
Exterior Column in C-C Panel Load Case: Combination-1
Load Case: Combination-1
Column Shear Type
Shear in Kip Shear in Kip
Same Localized Beams
Same Localized Beams (Through Panel C-C)
(Through Panel C-C)
B317 B297 B277 B257
(5th to 6th Floor) (4th to 5th Floor) (3rd to 4th Floor) (2nd to 3rd Floor)
(Gr. to 1st Floor)
(1st to 2nd Floor)
(2nd to 3rd Floor)
(3rd to 4th Floor)
(4th to 5th Floor)
(5th to 6th Floor)
(Gr. to 1st Floor)
B140 (1st to 2nd Floor) B12
3-D Model 2-D Model
14.735 -24.857 27.992
5.025 -0.075 0.075
56.174 60.135 Fx
Table 4.3Column Axial Force (-ve): 2-D vs Equivalent Frame Method
Story Height in ft
A.F from Software Analysis (2-D Model, Fz)
A.F from Equivalent Frame Method in Kip
In our analysis we have got results for different conditions, we desired. Necessary results are shown in the â€œchapter-5: Results & Comparisonsâ€?. In this chapter we have made various comparison tables, comparing graphs to execute our main purposes. The comparisons will give the scope to discuss about whole structureâ€™s behavior under different conditions considered. Comparing the moments across the entire structure shows that the moments obtained by considering 2-D model may be compared favorably with measured moments in the center bay of panels (panel C-C) in case of 3-D model. The difference at the negative moment section can be ascribed to as a difference in the stiffness of the columns is not assumed in the analysis or to as change in the property for 3-D model. AF (Axial Forces) computed by the proposed frame analysis (by Equivalent Frame Method) are generally in agreement with the measured AF by the software in case of 2-D model in the considering same direction (Fz). Although differences exist at individual sections, the over-all agreement is the best of any of the computed AF. The analysis of a flat slab by two-dimensional (2-D) Equivalent Frame Method is at best only a good approximation. It can be seen that the axial force obtained by the proposed frame analysis are in good agreement with those obtained by plate theory automated
in the analysis software. Although a two-dimensional frame analysis should not be expected to give the exact moments in slabs, it does give the values which are sufficiently accurate for design purposes. The comparisons show that even though the moments obtained by the proposed frame analysis differ from measured moments at some sections, the agreement is generally good. However, with this slight dissimilar outcome it is also apparent that variations of the slab stiffness, loading arrangement, and support conditions in the third dimensional (3D) analysis will influence the moments in the direction considered. The influence of these variations can be studied by the use of the theory of flexure for plates for 3-D model using digital computer based programs developed based on some reliable method such as â€˜Finite Element Methodâ€™ or on other available methods, but where there are no rigorous method is available for determining their effects by a two-dimensional analysis. This study involves the quantitative comparison of moments in reinforced concrete slabs as determined by the analysis of equivalent two dimensional elastic frames, by analysis based on the theory of flexure for plates, and by tests on both elastic and reinforced concrete models. In the first portion of the investigation moments determined from the analysis of equivalent frames are compared with the moments based on plate theory (based on FEM).
However, though we have obtained some slight differences in the resulted values. This is because of difference between methods for calculation used software and approximate analytical hand calculation. For instance, here the A.Fs from EQV.FM are calculated by hand with lower precision, and on the other hand, this analysis software is prepared based on FEM with higher precision & to have with all the compatibility of structures, thus the comparative A.F values are deviated. Finally, it can be said that, the variations of resulted values may be negligible to consider this analysis outputs for further proceeding design or decision to be made for further analysis.
06. Details of study on Beam deflection by software ABAQUS
Introduction ABAQUS is a powerful finite element software package. It is used in many different
fields throughout the world. ABAQUS performs static and/or dynamic analysis and
simulation on structures. It can deal with bodies with various loads, temperatures, contacts, impacts, and other environmental conditions.
ABAQUS includes four functional components: •
ABAQUS is a highly sophisticated, general purpose finite element program, designed primarily to model the behavior of solids and structures under externally applied loading. ABAQUS includes the following features: •
Capabilities for both static and dynamic problems
The ability to model very large shape changes in solids, in both two and three dimensions
A very extensive element library, including a full set of continuum elements, beam elements, shell and plate elements, among others.
A sophisticated capability to model contact between solids
An advanced material library, including the usual elastic and elastic – plastic solids; models for foams, concrete, soils, piezoelectric materials, and many others.
Capabilities to model a number of phenomena of interest, including vibrations, coupled fluid/structure interactions, acoustics, buckling problems, and so on. The abaqus.env is an environmental file available to users for use in configuring micro-
environments for running different jobs. When a user runs a certain job on ABAQUS, he/she may need to control various aspects of an ABAQUS job's execution. Variables called environmental variables are used to control the job's execution. These variables are assigned default values by the ABAQUS Site but the user can modify the environment file, abaqus.env, to run different jobs. For example, a user may: •
Change memory-related parameters to improve the performance of the job.
Control where and how scratch files are written.
Provide his/her own default values for some parameters to make operations easier.
Also many other aspects of a job's execution can be configured via the abaqus.env.When a job is submitted, ABAQUS will first search for the environmental file(s) in the following order:
1. The ABAQUS site subdirectory where abaqus.env defined by ABAQUS must exist. 2. The user's home directory where abaqus.env is optional and will affect all ABAQUS jobs submitted from user's account. 3. The current working directory where abaqus.env is optional and will affect all ABAQUS jobs submitted from the current working directory. Input Files The ABAQUS input file is an ASCII file with an extension of .inp. This file helps users communicate with the ABAQUS analysis modules and it must be created first. As a general finite element package, ABAQUS has multiple built-in libraries. The four main libraries are: •
Each library implements many keywords with their required and optional parameters and data lines. These keywords and parameters are readable both by ABAQUS and by the user. In comparison with most computer languages, the construction of the ABAQUS input file is simple. The key is to select the correct keywords and parameters to configure the models and the analysis procedures. There are two kinds of input lines used in an input file: keyword lines and data lines. We have worked on a RCC beam by ABAQUS to show the deflection due to load.we applied to concentrated load at two points of beam on the bean and then analyze it.we wanted to compare the value of deflection with a theoretical(known) value. 6.2
Literature Review on ABAQUS Al-Taan and Ezzadeen (1995) developed a numerical procedure based on the FE method for
the geometric and material nonlinear analysis of RC members. A beam element with a composite layer system was used to model the structure. For the nonlinear solution, an incremental-iterative technique based on Newton-Raphson’s method was employed. Only the displacement components were considered as DOFs where a parabolic interpolation function for axial displacement, and cubic interpolation function for other displacement was used. The numerical
solutions of a number of reinforced fibrous concrete beams were compared with published experimental test results and showed a good agreement.
To see the monotonic behavior of RC beams and beam-column assemblages, Kwak and Filippou (1997) introduced a FE model. In this model, concrete and reinforced bars were represented by separate material models. Another model was used between reinforcement bars and concrete to describe the behavior of the composite RC material. The concrete was modeled by eight-node elements with 3Ă—3 Gauss integration. The reinforcement was modeled by the two-node truss element. Between these two, a bond link element was used. Improved cracking criteria derived from fracture mechanics principles was used asthe basis for developing this smeared finite- element model.
Later Kwak and Kim (2002) introduced a new FE model for beams based on the moment-curvature relations of RC sections including the bond-slip and tension softening branch. They used the well established Timoshenko beam theory in the analysis. Bhatt and Kader (1998) presented a 2D parabolic isoparametric quadrilateral FE based on the tangent stiffening method for predicting the shear strength of RC rectangular beams. Wang and Hsu (2001) developed the FE analysis program FEAPRC from FEAP by introducing a new set of constitutive models for analyzing RC beams. The fixed-angle softened-truss model (FA-STM), which assumes cracks develop along the direction of principal compressive stresses applied at initial cracking, and that cracks are fixed at this angle thereafter, was used in the new set of constitutive models. The numerical results for beams, panels and framed shear walls were compared with the experimental results. Recently, Abbas et al (2004) presented a 3D nonlinear FE model for RC structures under impact loading. They used an elasto visco-plastic two surface model in the FE. The reinforcement was smeared as a two dimensional membrane of equivalent thickness. The layer was assumed to resist only the axial stresses in the direction of the bars. A simply supported beam with dynamic point loading was considered for numerical verification. Then experimental and numerical analyses were done on a circular plate with impact loading. Considerable work has been reported in recent literature relating to the development and application of FE procedures for RC slabs, plates, panels, and shells. Vecchio (1989) developed a nonlinear FE procedure to predict the response of RC structures. A smeared crack approach was included for concrete. A secant stiffness approach was used in the procedure incorporating the constitutive relations for concrete. Only low order FE analysis was used in the procedure. Numerical results were verified with the experimental data for square panels, deep beams and perforated walls. Later Polak and Vecchio (1993) modified the FE model for analysis of RC shell structures. In this adapted model,
a 42 DOFs heterosis type degenerate isoparametric quadrilateral element was developed using a layered-element formulation. During the same time, Vecchio et al. (1993) investigated the thermal load effect on RC slabs by nonlinear FE analysis. In the FE analysis they considered the concrete tension stiffening effect. Hu and Schnobrich (1990) derived a set of constitutive equations suitable for incremental FE analysis, and developed a nonlinear material model for cracked RC structures. This model was able to describe the post cracking behavior of RC structures. Reinforcement was treated as an equivalent uniaxial layered material placed at the depth of the centerline of the bar. For concrete nonlinear behavior, Saenzâ€™s (Saenz and Luis, 1964) stress-strain curve was used. The model considered smeared crack representation, rotating crack approach, tension stiffening, stress degrading effect for concrete parallel to the crack direction, and shear retention of concrete on the crack surface. The model was verified against a set of experimental data of RC panels. Cerioni and Mingardi (1996) introduced a FE model for analysis of a RC foundation plate, where the RC plate was modeled with materially nonlinear layered FEs.
Jiang and Mirza (1997) developed a rational numerical model for the nonlinear analysis of RC slabs. Material nonlinearities for both concrete and steel were considered. In the model, a RC slab was first divided into a number of composite elements, and each of the composite elements was then assembled into a single concrete plate element and a small number of steel beam elements. Kirchhoff thin plate theory was used in the plate element. Very recently, Phuvoravan and Sotelino (2005) presented a FE model for nonlinear analysis of RC slabs that combined a four node Kirchhoff shell element for concrete with two-node Euler beam elements for the steel reinforcement bars. A rigid link was considered between these two element types. This model takes care of the exact location of steel reinforcement bars.
Over the last decade, civil engineers have become very interested in the use of FRP due to its positive characteristics over the steel reinforcement. A large number of experiments on the topic were done in this time period. Many researchers also focus on the development of finiteelement models for the analysis of FRP RC structures. Shahawy etal. (1996) used a 2-dimensional non-linear FE computer program for analyzing beams strengthened with carbon fiber reinforced plastic (CFRP).
Nitereka and Neale (1999) developed a nonlinear FE layered model to predict the complete loaddeformation response of RC beams strengthened in flexure by composite materials. This model considered both material and geometric nonlinearities. The numerical results confirmed the
effectiveness of using externally bonded fiber reinforced composite laminates as a viable technique for strengthening concrete beams in flexure. Ferreira et al. (2001) presented an FE model for analyzing RC beams with FRP re-bars. They used the first order shear deformation theory in the analysis of concrete shells reinforced with internal composite unidirectional re-bars. The concrete was modeled with smeared crack concepts. A perfect plastic and a strain-hardening plasticity approach were used to model the compressive behavior of the concrete. A dual criterion for yielding and crushing in terms of stresses and strains was considered. For tension in concrete, the influence that the cracked concrete zones had on the structural behavior was considered. Smeared crack model was used. The response of concrete under tensile stresses was assumed to be linear elastic until the fracture surface was reached. A sudden and total release of the normal stress in the affected direction, or its gradual relaxation according to the tension stiffening diagram was adopted after cracking had occurred. Cracking in two principal stress directions in the plane of the structure was considered. In this model, the reinforcing bars were modeled as layers of equivalent thickness, having strength and stiffness characteristics in the bar direction only. In tension, it is elastic up to failure. The FE was implemented in the degenerated shell element by considering the theory discussed above. The model was verified against the experimental data for simply supported concrete beams reinforced with composites re-bars. A good agreement between the experimental and numerical results for beams was obtained. Supaviriyakit elal (2004) developed a FE model to analyze RC beams strengthened with externally bonded FRP plates. The concrete and reinforcing steel were modeled together by 8-node 2D isop plane stress RC elements. The RC element considered the effect of cracks and reinforcing steel as being smeared over the entire element. Perfect compatibility between cracked concrete and reinforcing steel was considered. The FRP plate was modeled as a 2D elasto-brittle element. As the epoxy is usually much stronger than the concrete, it was assumed a full compatibility between FRP and concrete. The model was verified against the experimental data of load-deformation, load capacity and failure mode of the FRP strengthen beam. Fanning (2001) used commercial software ANSYS to analyze reinforced and post-tensioned concrete beams. Hu et al. (2004) introduced a proper constitutive model to simulate nonlinear behavior of RC beams strengthened by FRP. They used the FE program ABAQUS. Reliable constitutive models for steel reinforcing bars and concrete are available in the material library. Only the nonlinearity of the FRP was added to ABAQUS as an external subroutine by the researchers. To model the nonlinear in-plane shear behavior, the nonlinear stress-strain relation for a composite lamina suggested by Hahn and Tsai (1973) was adopted. Tsai and Wu (1971) failure criteria were also used in the model. During the FE analysis, aperfect bonding between FRP and the concrete was assumed. The model was verified for load-deflection data of RC beams strengthened by FRP.
Step-by-Step Description of Working Procedure in ABAQUS: It is a abaqus software.In the software we design column & beam.It is an advance software.In
our thesis paper we design beam by using abaqus software.By using abaqus software we only design beam & column.Here we design beam. >Here is our design procedur:1. At first, length=3.6m Width=0.17m, & depth=0.26m, We draw a beam.(fig-1) 2. Then propertyedit material--then name—concrete& elasticyoung modulus2.25*10^10 N/m2 & poission ratio 0.2 then ok. 3. Concrete sectionsection 1concretesolidhomogenouscontinue then coming dialog box then thickness1 then ok. 4. Assign section.(fig-2) 5. Then part1—surf1Rebar1 then continous & choose surface select.(fig-3) 6. Then edit materialmaterial namesteel—elastic elastic—young modulus 2.1*10^11N/m2 & poission ratio 0.3, 7.
boxmaterialsteelmembrane thickness 2.5” & 0.635 give to draw Rebar layer setup. Rebar layer
Area per bar
Spacing orientation angle
8. Part1surface2Rebar2surface select then done. 9. Concrte sectionsteel1Shellmembranecontinue—surfacerebar layer—Same as. 10. Again surface-3rebar3—Surface select. 11.Again go to create sectionshellmembrane thickness 0.0635 & left side rebar layer setup.
Area per bar
12.Again same as 10 &11 repeat then right side. 13.Rebar reference orientation & datum setup. 14.For steel & concrete we put the plastic plastic value. 15.assemblydependentok.(fig-4) 16.Loadload managerCreat loadPressurecontinue. 17.Then select the surface & put the magnitude value 10Mpa & then click. 18.Boundary conditionDisplacement notationcontinue. 19.Meshselect partseed partglobal seed(global size2.5)ok.(fig-05) 20.Element typeelement type—C308k. 21.Mesh partyes.(fig-6) 22.Job manageredit joboksubmit.(fig-07) 23.Show cracking shape in (fig-08) 24.We find a deflection vs time show in (fig-09) These corresponding identical figures are as likely below:-
Modeling and Analysis by ABAQUS
Model Data: We modeled a RCC beam which, Length=360cm Width=18cm
Height=17cm Re bar orientation: Top surface=3nos Bottom surface=2nos
Model of the Beam in ABAQUS:
Figure 6.2(a) 3-D Model View from ABAQUS after modeling
Figure 6.2(b) 3-D Model View from ABAQUS after introducing material property
Figure 6.2(c) 3-D Model View from ABAQUS after Meshing the Beam Resulted Views after Analysis:
Figure 6.2(d) Deformed View after Analysis with Legends
Figure 6.2(e) General Cracking View after Analysis
Comparison Curve: The graph is drawn against Time VS Deflection based on the analysis outputs is represented below:-
Time VS Nodal Deflection
As a whole, it can be concluded that, the main purpose of the study to analyze a Flat Plate structure with its 2-D & 3-D model by software and conventional hand calculation methods and to make various comparisons between them is executed successfully. The column moments, plate node moments and A.F (axial force) of the considering column at different locations are successfully determined. Where, all of the outputs of the analysis have expressed the behavior of Flat Plate Structure and its structural philosophy. Also, all the purposes and scopes of this study including beam deflection using software ABAQUS are completed successfully. Where, by ABAQUS, we have successfully analyzed the model. After analyzing the model, we have found the deflected shape of the beam, the highly stressed portion and cracking portion of beam. We also found out the ‘Time versus Deflection’ curve. So, these précised outcomes can be used in any recognized or desired purposes.
08. Future Recommendation
Based on the lesson and knowledge of our thesis and project work, we may recommend the followings as future provision: 1. Flat Plate analysis may be done in other available methods, such as- FEM, ELM etc to make Flat Plate analysis so much realistic and effective. 2. The details of design procedure & design of Flat Plate based on our analysis report may be possible in the future. 3. The Flat Plate structures may be analyzed with some sophisticated software, such asMIDAS GEN, ANSYS and MIDAS CIVIL etc. to make the analysis more reliable & dependable. 4.
An automatic software using programming language VISUAL BASIC based on our study report and other trusted publications may be made as an entry to new era for analyzing & designing the Flat Plate structures only.
5. This study report may be repeated by others for only to verify and discover the variation of column moments and plate node moments in the same positions for various floors. 6. Column-to-Column joint behavior for different floors in case of Flat Plate structure analysis through our assumptions and theorems may be the topic for the upcoming students or fellows. 7. Deflection of various types of beams can be studied by approximate analytical hand calculation and by the sophisticated software to compare.
In reinforced concrete buildings, slabs are used to provide flat, useful surfaces. A reinforced concrete slab is a broad, flat plate, usuall...
Published on Nov 9, 2015
In reinforced concrete buildings, slabs are used to provide flat, useful surfaces. A reinforced concrete slab is a broad, flat plate, usuall...