Site Report 2- Steel
Professor: Dana BUNTROCK
GSI: Benjamin Michael LUECK
Student: Di (Carina) SONG
Background: The site is one of Kaiser Permenante’s properties and the project is a health care project. The design stage of the project lasts for 4 years with 3 years under review by state authority based on IBC and safety standards. Design standard of hospital will be relatively high compares to residential house. The main hospital building is rated as OSHPD Type 1, as it will provide in-patient care and overnight stay. The building’s mechanical and electrical systems were all calculated and tested for seismic issue. Master plan of this building is approved by the city of Oakland in 2006.
The differences between wood and metal construction seen in a big picture: -Machines: Different from wood construction site where materials are easily delivered by trucks, metal construction calls for the aid of cranes, either tower or mobile. Also, tools being used on site are different, as in wood site, the most seen tools are saws and nail guns, while in steel construction site, the common seen tools are pneumatic hammers, wrenches, wielders, and drills. This is because of their different fastening methods and material properties. (Edward Allen, 2008, p425) -Labors:
Wood site works are easier for single workers to manipulate, while the accomplishment of steel construction usually requires cooperation between workers. For example, if not using a tension control bolt or a wedge bolt, conventional bolts need a second worker with a wrench to prevent the other end of the bolt assembly from turning during tightening. Also, when putting the columns in the right position with cranes, ironworkers will collaborate with either the worker in cranes or other ironworkers. (Edward Allen, 2008, p428) -Prefabricated and Precise Considering the high density and weight of metal, it’s not an easy thing to lift the column up and cut it on site. And wielding on site is far more expensive than in a fabricator’s shop. Thus, most of the cuts, wields and angle bolts are made in fabricator’s shop before the materials are delivered on site. Careful and precise calculations of where to drill holes, where to cut and what angles to cut into, etc., are made prior to assembly by experienced fabricators, architects and engineers. (Edward Allen, 2008, p441) While in wood construction, for example, though workers need to nail the sheathing board on studs according to prescribed spacing, in reality, as far as I saw on site, they do not usually nail in such a precise way. However, metal requires precise holes location; otherwise, columns and beams won’t be bolted together. Other differences as mentioned in lecture, would be fire resistance, water proofing, termite, etc.
Despite the load bearing structure in metal construction site, the partition wall structures in metal construction has a lot in common with wood construction. Interior partition walls of the visited metal site uses light gauge steel construction which is considered as â€˜the noncombustible equivalent of wood light frame constructionâ€™. (Edward Allen, 2008, p490) This report will be divided into two parts. The framing methods of the load bearing steel frame will be f discussed first, where certain connections would be illustrated. Then, the second part will focus on the partition walls which use the light gauge steel construction method.
Grade beams meshes downpipes are set within the trenches before concrete are poured in Rectangular arrangement of vertical bars and column ties. Vertical bars have larger diameter while ties are in smaller diameter. Moisture weather is good for concrete curing, as the hydration in air will keep moist in concrete until its required strength is achieved. Thus there are no extra shade or evaporation retarders covering the concrete. Windy and hot weather is not ideal for curing concrete. Common concrete curing date is 28days.
Formwork can protect the moisture in concrete from evaporating. For those top surfaces, spraying or flooding water is required over the concrete surface. (Edward Allen, 2008, p527) Formwork is established for keeping the shape of concrete and it is taken off once concrete is cured sufficiently. (Edward Allen, 2008, p528)
Concrete resists compression while reinforcing steel resists tension. In North America, reinforcing bars are made almost entirely from recycled steel scraps, primarily junked automobiles. (Edward Allen, 2008, p521)
Concrete Welded wire reinforcing (overlap) Vapor retarder Crushed stone for drainage and layered surface Formwork brace
This is a pile that is dig 90 feet, and the pile is connected to foundation with a seismic isolator in between.
After establishing the foundation, erection of multistory steel building frame starts with the erecting of the first two story tier of framing. Columns are lifted to site by cranes and placed in position. Then beams and girders are connected to columns above the middle point of every column.
Back up bars for clean welding
The structural columns are wide flanges with sprayed fire proofing materials. Base plate
Connection 1 is a single â€“tab moment connection.
Leveling nuts support the base plate before grouting
A shear tab is welded to the column in the shop, and the beam is bolted to it on the construction site to hold beam in place. Then workers will weld one side of the beam flanges on site. (Edward Allen, 2008, p437)
Connector plate welded to the column in shop
Buckling restrained brace ( BRB)
Steel tube encasing mortar The steel tube was casted with 3000psi concrete. The system will absorb Wide Flange energy by crushing the concrete surrounding. will steel reduce theinside WithThis yielded core earthquake force within the building as a whole. ( Dana, lecture on 03/08/2012) L angle Gusset plate The joint is designed to be relatively weak compared to other joints in the building. So when the building fails in an earthquake, these joints fail first. This ensure the confidence of failure prediction increases reduces Cast and within steel the global failure.
Metal plate Column and gusset plate are welded to the base late before grouting BOTTOM Buckling restrained brace No welding, subjected to rotation
Middle of one tier
Columns in metal construction site always erect two story high tiers. After the first tier is erected and beams being bolted into place, there will be a temporary wood plank laid over the framing. Then the second tier will be attached to the first tier.
The building uses eccentrically braced frame where the ends of the diagonal braces offset some distance, aiming to absorb seismic energy. (Edward Allen, 2008, p435) As observed in the connection of first pier, brace bottom joints are shear connection while brace top joints are moment connection.
One end of the metal plate was welded in shop with the other end weld on site
Not only the exterior of the building frame are braced, the interior is also braced with eccentrically braces. Joints can be seen as illustrated below. The number of bolts varies according to the load that each part would bear. (Photo 1, 2) Second tier
In 5th floor where all the mechanic systems are located, stronger braces are used, as the equipment adds up the live load of this floor. (Photo 3) 1
Erection of upper tiers follows the same workflow as for the first tier. First put column in position-partially boltconnect beams and girders- tighten the bolts- brace up- cover working plank over tier top. Then further tiers would be installed with the help of cranes.
FLOOR AND ROOF DECKING The main floor structure used on site is metal decking. Single corrugated sheets are commonly used for roof decking, where concentrated loads are not great. Metal decking is used as a permanent formwork for concrete floor. (Edward Allen, 2008, p453)
Metal decking joist
Metal decking is usually welded to the joists beams and girder. However, in the visited site, part of metal decking is bolted to the beams.
Beam to beam connection
There are signs of welds on the overlaps of two pieces of metal decking.
areintwo proofing isThere welded thetypes shapeofofweather hollow core in materialsstronger seen onstiffness site: oneand is durable achieving strength. polypropylene shrink wrap system, and the The gapisbetween other xypac. pipe and floor is also sealed to prevent water from the Chemical reactions between the admixture structure. and the concrete will produce a cryslline structure within concrete to protect water from infiltration. 6
Temporary supports are inserted within floors to secure partially cured concrete floor slabs. This is called reshoring. Vertical members of the reshore are connected down on the cantilevered beams that are clamped down by scaffolds. The whole system shore over 4 floors and itâ€™s very labor consuming.
Fire Resistance for Metal Structure
In a fire event, fire will weaken metalâ€™s structural stability. For taller building, fire resistance is necessary to protect the steel frame from heat for longer evacuation time. The visited building uses spray- applied fireproofing, which is the most commonly applied method in field after the steel have been erected. (Edward Allen, 2008, p463) The building also uses double layered gypsum board for longer fire rating purpose. As commonly single layer gypsum board has 1 hour rating, doubled layer will give a 2 hour rating. Bulk insulation within the studs will achieve better thermal performance.
Light Gauge Steel Construction Within the partition wall system, light gauge steel frame works similar as wood light frame constriction. They both use studs and joists and share the similar sizes and spacing. As seen in the above picture, steel studs can be sheathed and insulated.
Two studs welded together
Light gauge steel members are joined together with self-drilling; self- tapping screws by hand drills. Skewers are coated with zinc to resist corrosion. Welding might be needed when particular stronger connections are needed.
The steel used in light gauge construction is coated with zinc or aluminum â€“zinc alloy to avoid rust. Studs, joists and rafters are formed into C sections. The size and thickness of steel varies. The webs of the members are punched with holes at inches intervals. This will allow wires, pipes and braces to go through members easily, minimizing the amount of holes to drill on site. (Edward Allen, 2008, p490)
Door openings are framed by steel studs anchored to the runners.
Services & Facilities
After the building frame is established, services and mechanical facilities are moved into the building. Prior to the construction of floor decking, calculation of detailed location of each plant is required, as wires, pipes are going to go through the floor system. On the site, steel strips hanging down from ceiling are used to mark location of wires. Electrical boxes are fixed to the studs as it is the same with wood frame constriction.
In conclusion, this steel construction site demonstrates various connections and joints of steel for different purpose. The building stands up by adding tiers upon each other. In the event of an earthquake, eccentric bracing will effectively integrate the building into a stronger system. The interior light gauge steel frame is similar to wood light frame construction.
Considering the properties of material where steel is harder to be drilled and less economically to be welded on site, thorough consideration of design before site-work is crucial.
Bibliography Aleen Edward, Fundamentals of building construction materials and methods, Wiley,2009 Ching, Frank. Hoboken, Building codes illustrated : a guide to understanding the 2006 International building code , New York, Wiley, c2007 Chudley, R.,& Greeno, R., Building Construction Handbook, 4th edition, Oxford, ButterworthHeinemann, 2001