EVALUATION OF STRUCTURAL IRREGULARITIES IN RCC STRUCTURES

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EVALUATION OF STRUCTURAL IRREGULARITIES IN RCC STRUCTURES Snehal Kshirsagar1, Shidhi swarupa Nayak2 Assistant Professor, Dept. of Civil Engineering, Sanghavi college of Engineering, Maharashtra , India Assistant Professor, Dept. of Civil Engineering, Sanghavi college of Engineering, Maharashtra , India ---------------------------------------------------------------------***--------------------------------------------------------------------Masonry units, which are made of clay bricks and/or Abstract-

concrete blocks, are used primarily for their affordability and ease of use in construction. Mortar is a necessary material used to bind individual masonry units in masonry construction. Sand is combined with a binding substance to create mortar. Most seismic-resistant structural design processes view the masonry infill wall that is used with an RC frame as a non-structural component of the building.

Consequently, this comprehension leads to an inaccurate estimation of the RC frame's lateral stiffness, ductility, and strength. Because of the lack of knowledge regarding the behaviour of infilled RC frames, the difficulty of conducting a structural analysis, and uncertainty regarding the relationship between infill walls and RC frames, a number of researchers were reluctant to consider the contribution of masonry infill units. The damage that occurred in RC frame buildings following earthquakes actually demonstrated that the infill masonry wall may have been a major factor in the structural seismic resistance, as RC frame buildings with masonry infill walls have borne greater seismic forces than bare frames (frames without masonry infill wall). In RC frame buildings, the performance of masonry infill walls has been experimentally investigated by numerous researchers.

According to experimental findings, the composite action between the RC frame and masonry infill wall as well as the amount of lateral loads were related to the masonry unit's performance. The stiffness of the structural system is therefore greater than that of the RC bare frame. The masonry units begin to fracture and slip at the interface between the RC frame and masonry infill units at the tension zone as lateral loads increase. The masonry units, however, create a diagonal strut action on the compression zone. The primary objective of this research is to better understand the behaviour of all building frame components by examining the presence of masonry walls in structures that are subjected to seismic loads. In order to shed light on the structural performance and direct the new provisions in the development of logical design rules, numerical simulations are crucial.

Seismic analyses typically overlook infill walls, which are frequently used in R.C. buildings, because they are assumed to be non-structural components. A general review of various expressions put forth by researchers to determine this equivalent width of the diagonal strut is presented in this paper. The fundamental factor influencing the stiffness and strength of these struts is their equivalent width. On the other hand, infill walls help the building's lateral stiffness and seismic resistance. An attempt is being made in this study to incorporate the masonry infill in the form of an equivalent diagonal strut, the width of which is determined by the different relations that the researchers have proposed. In order to determine the width of the equivalent diagonal strut, a general review and comparison of the relations suggested by the researchers is being conducted.

The purpose of this study is to compare the equivalent width of a diagonal strut calculated manually and with software Using ABAQUS software.

Key Words: R.C. frame, Infilled wall, Equivalent width of diagonal strut, ABAQUS Software.

1. INTRODUCTION The most popular building design in developing nations like India is RC moment-resisting frames. Buildings with RC moment-resisting frames are made of moment-resisting frames with masonry walls as infills. According to building practices, these walls are regarded as non-structural components. Modern building design practices disregard the impact of infill masonry walls and treat them as nonstructural components, instead designing buildings as framed structures. When compared to buildings with only moment-resisting frames, buildings with infill walls behave differently for the reasons mentioned above. Through numerous analytical and experimental investigations over the past forty years, the significance of brick infill has been acknowledged; however, because it is regarded as a nonstructural element, its strength and stiffness contribution has been overlooked.

The distribution of stiffness, mass, plan, strength, and numerous other irregularities in the structure's vertical and horizontal directions determines how the structure will behave during an earthquake. Previous building damage scenarios showed that irregularities were a major factor in the structures' failure during intense ground shaking. When an earthquake occurs, the structure generates horizontal forces, which result in inertia forces acting through the

In this paper, the strength and stiffness of brick masonry infill are taken into consideration when modelling a masonry infill wall with a "equivalent diagonal strut." In nations that experience earthquakes, masonry infill walls are typically utilized as an infill (partition) in RC frame buildings.

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structure's centre of mass. The vertical columns and walls resist all of these forces, and the centre of stiffness is the point through which the forces act.

equation 8 and 9. The application of the formula on infilled RC frame structures of 2-6 storey showed that the behavior of strut models correspond to that of the shell element model.

During intense ground shaking, the degree of horizontal and vertical irregularities has a significant impact on the performance of the structure. A structure must have sufficient lateral strength, a straightforward and regular design, and enough stiffness and ductility in order to withstand seismic forces. Structures with uniform mass and stiffness in plan and elevation, as well as simple geometry, are less susceptible to damage than those with irregular configurations. In some ways, many building structures are asymmetrical. Some were intentionally designed that way, while others developed this quality by chance.

Dillon S. Lunn, Sami H. Rizkalla they studied that the evaluates the effectiveness of different externally bonded glassfiber–reinforced polymer (GFRP) systems for increasing the out-of-planeresistance of infill masonry walls to loading.

The research included a comprehensive experimental program comprising 14 full - scale specimens, including four strengthened (control) specimens and 10strengthened specimens. To simulate the boundary conditions of infill walls, all specimens consisted of a reinforced concrete (RC)frame, simulating the supporting RC elements of a building superstructure, which was infilled with solid concrete brick masonry. The specimens were loadedout – of – plane using uniformly distributed pressure to simulate the differential (suction) pressure induced by a tornado.

Parameters investigated in the experimental program included aspect ratio, FRPcoverage ratio, number of masonry wythes, and type of FRP anchorage.

2. OBJECTIVES: 1.

2.

3.

4.

To obtain general diagonal strut width by using software SIMULIA ABAQUS. To get the width dimensions of strut to check the out response of high story building with and without structural irregularities and compare the result of both with each to check their structural behavior in form of base shear, nodal displacement.

To study and analyze the evaluation of structural irregularities in RCC structure under seismic loading in static condition.

Compare the results with those of available in literature and validate the theory.

Liu Ming, Cheng Yun, Liu Xiawei they studied that the behaviors of infill wall in earthquakes show that infill masonry walls,which are used as nonstructural elements of concrete frames, are vulnerablewhen they are subjected to earthquake. In order to achieve an optimal anti seismic behavior, or even stability, two methods of connection are investigated. The shaking table tests, with 1:3 scale walls of two-storey model subjected to horizontal earthquake loads, were carried out to investigate the out – of – plane behaviors with different connections between walls and beams. The test results show that the connection methods employed between walls and beams have a significant effect onthe out-of-plane stability of infill walls.

3. LITERATURE REVIEW : Bharat Pradhan, Maria Zizzo, Vasilis Sarhosis, Liborio Cavaleri they have studied that extensive literature regarding the Out-of-Plane tests on infill walls has been reviewed with a detailed comparison of the experimental results based on different influencing parameters (slenderness ratio, aspect ratio, boundary conditions, openings, vertical load. In-Plane damage, strength of masonry and plaster, frame stiffness).

4.METHODOLOGY: To study the effect of earthquake on a high-rise RC framed structure by considering different irregularities in earthquake seismic zone IV as per IS code 1893 (Part I):2002.

Panto B, Silva L, Vasconcelos G, Lourenço PB they studied that the numerical simulation of two solutions of brick infill wallsdeveloped at University of Minho under out – of – plane loading. The numerical simulation is based on an innovative discrete macro-modelling strategy proposed by Caliò and Pantò (2014). This method is based on a hybrid approach by which the frame is modelled using concentrated plasticity beam-column elements, whereas the non-linear behaviour of masonry infill is modelled by means of a 3D discrete macroelement.

Following steps of methods of analysis are adopted in this study: Step-1: Selection of the structures with different irregularities.

Step-2: Selection of seismic zone (IV).

Step-3: Formation of load combinations.

Step-4: Modelling of building frames using ABAQUS software.

Step-5: Equivalent static Analysis of all the models.

Step-6: Comparative study of results (seismic parameters) in terms of width of diagonal strut, stiffness of infilled wall, pushover curve.

Ida Ayu Made Budiwati, Made Sukrawa. In this paper, they have studied that Based on results from numerical analyses the following formula for the equivalent width of diagonal strut of infilled frame with reinforced opening is proposed in

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5. STRUCTURAL MODELING:

1) Static load apply in wall

Problem statement:-

static load

A 10 storeyed moment-resisting RC framed building having the plan dimensions of 15m X20m with bay length of 5m in both directions and floor height of 3.2m as shown in figure.

Is considered in the study.

Column and beam size (based on preliminary design) 1st to 4th floor = 350mm X 750mm.

5th to 7th floor = 300mm X 600mm.

8th to 10th floor = 230mm X 450mm.

Beam size = 230mm X 450mm.

Thickness of slab = 125mm.

The structure is modelled as 3D frame using ANSYS . The masonry infill is modelled as equivalent diagonal strut member, quadrilateral shell element and as membrane element (with in plane stiffness) of uniform thickness (230mm).

Fig. 3.2.1 static load apply in wall The structure is analysed for the seismic loads and load combinations as per the Indian standards, IS -1893 (Part -1)2002; Seismic zone = Zone V

Properties of the concrete :Modulus of elasticity = 25000 MPa. Poisson’s ratio = 0.2 Grade = M25(25 MPa) Density = 25 KN/m3.

Mass per unit volume = 2.55 kg/m3.

Importance factor =1 Soil type = II Live load = 10,20, 30, upto failure (KN/m2)and designed as per IS 456-2000.

Properties of the reinforcement steel:Modulus of elasticity = 210000 MPa. Poisson’s ratio = 0.3 Grade = Fe 415 (415 MPa)

Full dead load (self – weight ) and 25% of live (imposed) load constitute the seismic weight as per IS-1893 -2002.

As per mentioned problem the columns and beams are modelled beam elements and the slab as the rigid diaphragm the masonry infill walls are modelled as the equivalents diagonal strut. The diagonal strut is modelled as “compression only” members in ABAQUS Software.

Properties of the masonary:Modulus of elasticity = 3500 MPa Poisson’s ratio = 0.2 Density = 20 KN/m3.

Mass per unit volume = 2.03 kg/m3 Loads on the structure: self –weight of frame (beams, columns, slabs), weight of infill walls, and live load (KN/m2) is considered for the analysis of the frame.

Note:- check at different live load values.

In the present work, seismic response of frames having different configurations are obtained numerically using a finite element based software, the major inputs are effective width of diagonal strut.

Fig – Plan and elevation of building

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6. RESULTS AND DISCUSSIONS:

Fig – Stresses induced in frame structure.

Fig- Modelling of infill wall.

Fig – Stresses induced in infill wall structure.

Fig – Modelling of frame structure.

Fig – Combination of frame and infill wall structure.

Fig – Load assigned on infill wall

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Demir sivri’s(2002)

and

0.136843

1.19E+04

2.08E+08

Mainstone’s(1971)

0.125624

1.19E+04

1.91E+08

Software analysis

0.340181

1.19E+04

5.21E+08

Fig – Width of diagonal strut in ABAQUS software.

7. CONCLUSIONS From the above conclusions it is clear that the regular structure with RC moment resisting frame and with masonry walls, perform better under the action of seismic load. The obtain general diagonal width of strut by using software SIMULIA ABAQUS is 1.30 and Area = 0.340181 m2. the stiffness of infill wall is 5.21E+08. the results are compared by other researchers theory it is concluded that as per the software results the width of diagonal strut dimension nearly validate to the theory of pauley and priestley’s. and are shown below; Table – 1: Comparison of width of diagonal strut Methods

Formula

Width of diagonal strut

Holmes(1961)

W=d/3

1.868

Pauley and priestley’s(1992)

W= 0.25d

1.401

Smith’s (1968)

W=1/2(αh+αL)^(1/2)

1.240

W=0.175(λH)^(0.4)(H2+L2)^(1/2)

0.547

Mainstone’s(1971)

W=0.175(λh)^(-0.4) *w

0.502

Software analysis

ABAQUS modelling

1.302

Demir sivri’s(2002)

and

Fig- Validate the manual and software results comparatively

Table – 2: Comparison of stiffness of infill wall Methods

Area =wt(m2)

Column Stiffness

Stiffness infill wall

Holmes(1961)

0.466908

1.19E+04

7.08E+08

Pauley and priestley’s(1992)

0.350181

1.19E+04

5.31E+08

Smith’s (1968)

0.310026

1.19E+04

4.7E +08

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Fig – Stiffness of infilled wall

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