seminar on steel plate shear wall

REPORT ON

STEEL PLATE SHEAR WALL

PRACTICAL DESIGN AND CONSTRUCTION

Guided by: Submitted by:

Prof.P.G.Patel Nilesh H. Saksena

EN.NO.:110280715004

Applied mechanics department

L.D.College of engineering

AHMEDABAD-15

Steel plate shear wall

INDEX

SR.NO. TITLE

1. INTRODUCTION

2. SYSTEMS OF STEEL PLATE SHEAR WALL

3. ADVANTAGED OF STEEL PLATE SHEAR WALL

4. DISADVANTAGES OF STEEL PLATE SHEAR WALL

5. USE OF STEEL PLATE SHEAR WALL AND THEIR SESMIC BEHAVIOUR

6. ANALYSIS AND DESIGN APPROACH

7. CONSRUCTION CONSIDERATIONS

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1. INTRODUCTION

The main function of steel plate shear wall is to resist horizontal story shear and overturning moment due to lateral loads. In general, steel plate shear wall system consists of a steel plate wall, two boundary columns and horizontal floor beams. Together, the steel plate wall and two boundary columns act as a vertical plate girder as shown in Figure. The columns act as flanges of the vertical plate girder and the steel plate wall acts as its web. The horizontal floor beams act, more-or-less, as transverse stiffeners in a plate girder.

Components of steel plate shear wall systems

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Steel plate

Horizontal floor beam

Boundary column


2.SYSTEMS OF STEEL PLATE SHEAR WALL:

1. Un-stiffened, thin SPSW: In these systems the shear wall is without provision of stiffeners.

Main component of unstiffened thin SPSW systems:

a. Steel plate: This element is usually a relatively thin steel plate. Plates thinner than 3/8 inch are not recommended since such thin plates cannot be easy to handle during fabrication and erection.

b. Boundary column: boundary column in the systems resist the gravity load and also provide resistance against large amount of torsional moments and give the anchorage to the steel plate.

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c. Horizontal floor beams: The top and bottom beams in a shear wall act as anchor for tension field action of the steel plate and also

provide support to the floor.2. Stiffened SPSW: In these systems the shear wall is provided

with horizontal stiffeners on one side and vertical stiffeners on other side.

3. Composite concrete SPSW: The composite shear walls consist of a steel plate shear wall with reinforced concrete walls attached to one side or both sides of the steel plate using mechanical connectors such as shear studs or bolts.

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Main Components of a Composite Shear Wall

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Main components of composite shear walls shown in Figure are steel wall, concrete wall; shear connectors, boundary columns, boundary beams, connection of steel wall to boundary beams and columns, and beam-to-column connections.

a. Steel plate shear wall: This element is usually a relatively thin steel plate. Plates thinner than 3/8 inch are not recommended since such thin plates cannot be easy to handle during fabrication and erection.

b. Reinforced concrete (R/C) shear wall: Reinforced concrete walls can be connected to one side of a steel plate shear wall. the R/C wallprovides shear strength and stiffness, through its compression field andsome ductility depending on the amount of reinforcement in the wall.

c. Shear connectors: Shear connectors are used to connect steel elements of the composite wall to concrete. For cast-in-place concrete usually welded shear studs are used. Of course other shear connectorssuch as channels can also be used although they may not be as economical as welded shear studs. For pre-cast concrete walls, bolts can be used to connect the R/C walls to steel plate walls

d. Boundary columns: In addition to gravity loads, the columns on the sides of a composite shear wall resist the bulk of overturning moments. The columns also provide an anchor point for tension field action ofthe steel plate and bearing element for compression diagonal element of the concrete wall. In structures with relatively large columns, the columns can also transfer a considerable amount of story shear.

e. Boundary beams: The top and bottom beams in a composite shear wall act as anchor for tension field action of the steel plate and as compression bearing element for compression diagonal of the concretewall.

f. Connections of shear wall to boundary members: The steel shear wall should be connected to boundary columns and beams either by

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bolts or welds. The main role of these connections is to transfer shear and tension. The concrete wall can also be connected to the boundary walls using mechanical connectors. These connections transfer shear that is resisted by the reinforcement inside the wall.

g. Beam-to-column connections: These connections play a major role in performance of the walls. In a dual system, where the steel frame is the “back-up” system for the composite shear wall, the connections should be moment connections

3. ADVANTAGES OF STEEL PLATE SHEAR WALL:

1. Wall Thickness. SPSW allow for less structural wall thickness in comparison to the thickness of concrete shear walls. Astudy performed for The Century project indicated an average wall thickness, including the furring, of 18” as opposed to a concrete shear wall thickness with anaverage of 28”. This resulted in a savings of approximately2% in gross square footage.

2. Building Weight. SPSW result in ales ser building weight in comparison to buildings that use concrete shear walls. A study performed for The Century project indicated that the total weight of thebuilding as designed using SPSW was approximately 18% less than that of the building designed using a concrete shear wall core system, which results in a reduction of foundation loads due to gravity and overall building seismic loads.

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3.Fast Construction. The use of a SPSW system reduces construction time. Not only is it fast to erect, but there also is no curing period. A scheduling study performed by a contractor for The Century project indicated a one-month reduction in construction time. The steel erector for the U.S. Federal Courthouse indicated that the erection of the SPSW was much easier than that of the special concentrically braced frames.

4. Ductility. A relatively thin steel plate has excellent post-buckling capacity. Research performed on the SPSW system indicates that the system can survive up to 4% drift without experiencing significant damage, even though most of the tests showed damage outsidethe steel plate panel. There was some pinching and tearing close to thecorners of the panel due to bending. However, this tearing did not reducethe plate capacity and stiffness.

5. Tested System. At least two buildings that use SPSW as their primary lateral force resisting system have undergone significant earthquake ground shaking. Both buildings survived with insignificant insignificantstructural damage (Astaneh & Zhao, 2002). The system also has been tested since the 1970s. The system has been recognized in the National Building Code of Canada (NBCC) since 1994 and will be included in the American Institute of Steel Construction (AISC) Seismic Provisionsin 2005.

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4.DISADVANTAGES OF STEEL PLATE SHEAR WALL:

1.Stiffness. SPSW systems are usually more flexible in comparison to concrete shear walls, primarily due to their flexural flexibility. Therefore, when using SPSW in tall buildings, the engineer must Provide additional flexural stiffness. In both The Century and the U.S. Federal Courthouse projects, large composite concrete infill steel pipe columns were

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used at all corners of the core wall to improve the System’s flexural stiffness as well as its overturning capacity.

2. Construction Sequence. Excessive initial compressive force in the steel plate panel may delay the development of the tension-field action. It is important that the construction sequence be designed to avoid excessive compression in the panel. In the U.S. Federal Courthouse project, the welding of the plate splice connections was delayed until most of the dead load deformation occurred in order to relieve the pre-compression within the steel plate shear wall panel.

3.New System. Due to unfamiliarity with the system, a contractor will typically estimate a relatively high erected cost. This may be solved by engaging the contractor early in the design phase.

5. USE OF STEEL SHEAR WALLS AND THEIR SEISMIC BEHAVIOR

Steel plate shear walls (SPSW) have been used, to a limited extent, as the primary lateral force resisting system in buildings for more than three decades. There have been numerous SPSW research programs in this timeframe in the United States, Canada, and Japan to help foster a

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better understanding of the system’s behavior, particularly as it relates to earthquake-resistant design. Some major building projects that utilized SPSW as the primary lateral force resisting system include the following:

➜ United States Federal Courthouse, Seattle, WA— 23-story building (350’)

➜ Sylmar Hospital, Los Angeles, CA— six-story building

➜ Canam-Manac Headquarters Expansion, St. George, Quebec— six-story building

➜ Hyatt Regency Hotel at Reunion, Dallas, TX— 50-story building (562’)

➜ The Century, San Francisco, CA— 46- story building (465’; the project was cancelled after the completion ofdesign and permit)

➜ Nippon Steel Building, Tokyo, Japan— 20-story building

➜ Shinjuku Nomura Building, Tokyo, Japan— 51-story building (693’)

➜ Kobe Office Building, Kobe, Japan— 35-story building (425’)

1.A 20-story office building in Tokyo, Japan

According to Thorburn et al. (1983) it is believed that this building, referred to as Nippon Steel Building, was the first major building using steel plate shear walls. Located in Tokyo, it was completed in 1970.

The lateral load resisting system in longitudinal direction was a combination of moment frame and steel plate shear wall units in an H

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configuration and in transverse direction consisted of steel plate shear walls.

Figure 2.1 shows a typical plan. The steel plate wall panels consisted of 9’ by 12’-2” steel plates with horizontal and vertical steel channel stiffeners.

Figure 2.2 shows the details of steel plate shear wall system. The thickness of steel wall plates ranged from 3/16” to ½” . In design, the gravity load was not given to steel shear walls and the walls were designed to resist design lateral loads without buckling.

2.53-story high-rise in Tokyo

The structure was initially designed using reinforced concrete shear walls. However, according to Engineering News Record (1978), due to patent problem, the R/C walls were converted to steel shear walls. Figure 2.3 shows a plan view and elevation of the building. According to

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ENR article (ENR, 1978), “the contractor rejected a steel braced building core as too expensive” compared to steel shear wall.

The structure consisted of moment perimeter frame and “T” shaped stiffened steel shear walls. The wall panels were about 10-ft high and 16.5 feet long and had vertical stiffeners on one side and horizontal stiffener on the other side. The panels were connected to boundary box and H steel columns using bolts. The construction contractor in this case has made a comment that “ The next high-rise building we do won’t likely be designed with bolted steel seismic walls” (ENR, 1978). According to ENR article, the contractor on another high-rise in Tokyo switched from bolted steel panels to welded panels after failing to achieve the required precision. .

3. A 30-story hotel in Dallas, Texas

This structure, described in Reference (Troy and Richard, 1988) is a very good example of efficient use of steel shear walls in areas with low seismicity but with relatively high wind loads. The 30-story structure has steel braced frame in longitudinal direction and steel plate shear walls in the transverse direction. The shear walls in this structure

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carry about 60% of the tributary gravity load while the wide flange columns at the boundary of shear walls resist the remaining 40%.

By using steel plate shear walls as gravity load carrying elements, the designers have saved a significant amount of steel in beams and columns and compared to equivalent steel moment resisting frame, the steel shear wall system has used 1/3 less steel (Troy and Richard, 1988). Located in Dallas, the wind loads were the governing lateral loads. Under the design wind load, maximum drift was only 0.0025. The relatively low drift is due to relatively high in-plane stiffness of steel plate shear walls. Figure 2.4 shows a view of the building.

4.A 6-story hospital in Los Angeles, California

This structure shown in Figure 2.5 is a good example of the use of steel shear walls in an “important” structure such as a hospital in an area of very high seismicity such as California. The hospital building is a replacement for the reinforced concrete Olive View

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Hospital that had partially collapsed during the 1971 San Fernando earthquake and had to be demolished.

In the new Sylmar Hospital, shown in Figure 2.5, the gravity load is resisted entirely by a steel space frame and the lateral load is resisted by the reinforced concrete shear walls in the first two stories and steel plate shear walls in the upper four stories. The steel shear wall panels in thisbuilding are 25 ft wide and 15.5 feet high with thickness of wall plate being 5/8” and ¾”.

The walls have window openings in them and stiffeners as shown in Figure 2.6. The steel plate panels are bolted to the fin plates on the columns. The horizontal beams as well as the stiffeners are double channels welded to the steel plate to form a box shape as shown in Figure 2.6. According to the designers, (Youssef, 2000) and (Troy and Richard, 1988) the double channel box sections were used to form torsionally stiff elements at the boundaries of steel plates and to increasebuckling capacity of the plate panels.

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The walls were designed for global buckling capacity of the stiffened walls as well as local buckling capacity of the panels bounded by the stiffeners. The tension field action capacity was not used although the designers acknowledge its presence and consider the strength of tension field action as a “second line of defense” mechanism in the event of a maximum credible earthquake.

5.A 35-story office building in Kobe, Japan

One of the most important buildings with steel plate shear walls in a very highly seismic area is the 35-story high-rise in Kobe, Japan. The structure was constructed in 1988 and was subjected to the 1995 Kobe earthquake. The structural system in this building consists of a dual system of steel moment frames and shear walls. The shear walls in the three basement levels are reinforced concrete and in the first and

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second floors the walls are composite walls and above the 2nd floor the walls are stiffened steel shear walls. Figure 2.9 shows framing plan and typical frames. The author visited this building about two weeks after the 1995 Kobe earthquake and found no visible damage.

6.A 52-story residential building in San Francisco, California

Currently, the tallest building with steel plate shear walls in a very highly seismic area of the United States is a 52-story building in San Francisco. The structure is designed by Skilling, Ward, Magnusson,

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Barkshire of Seattle and is currently under construction. The building is a residential tower and when completed will have 48 stories above ground and four basement parking levels. A rendering of the building and a typical floor plan are shown in Figure 2.12.

The gravity load carrying system in this building consists of four large concrete-filled steel tubes at the core and sixteen concrete-filled smaller steel tube columns in the perimeter. The floors outside the core consist of post-tensioned flat slabs and inside the core and lower floors are typical composite steel deck-concrete slab. The foundation consists of a single reinforced concrete mat foundation.

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The main lateral load resisting system of the structure consists of a core made of four large concrete field steel tubes, one at each corner of the core, and steel shear walls and coupling beams. There are built-up H columns between the two corner pipe columns. The steel shear wallsare connected to concrete filled steel tubes by coupling beams. The shear wall units are primarily shop-welded and bolt spliced at the site at each floor mid-height. The only field welding is the connection of the girders and steel plate shear wall to the large concrete-filled steel tube columns.

7. A 22-story office building in Seattle, Washington

A view of this building is shown in Figure 2.13. At this writing, (summer of 2000) the structure is being designed by Skilling Ward Magnusson Barkshire. A typical floor framing consists of typical steel deck/concrete floors supported on wide flange beams and columns.

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The lateral load resisting system consists of a core with four large concrete filled tubes on its corners and steel plate shear walls and coupling beams connecting the tubes to each other in one direction and steel braced frame in the other.

Similar to the 52-story structure discussed in previous section, the steel plate shear wall system in this building also is primarily shop-welded, field bolted with only steel plates and girders welded to the round columns in the field. Four round concrete-filled tubes carry the bulk of gravity in the interior of the building. The I-shaped columns within the steel box core do not participate in carrying gravity and are primarily part of the lateral load resisting system which can be considered to be a dual system of steel shear wall and special moment-resisting frames.

6. ANALYSIS AND DESIGN APPROACH

The typical SPSW system is comprised of steel plate panels, vertical boundary elements, and horizontal boundary elements.

The general procedure in the design of the SPSW system is as follows:

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1. Gravity Framing:

The building frames, including the SPSW boundary elements, should be designed to carry gravity loadings while neglecting the contribution of the SPSW panels. This is an important factor, done to ensure that the building frames have sufficient capacity to support the gravity loads during seismic events, during which the plate experiences buckling due to the development of its tension field action

2. Steel Plate Panel:

The steel plate panel is designed to handle both wind and seismic loads. All lateral shear loads in the SPSW panel are resisted by the steel plate, utilizing tension- field action. There are many different approaches that can be used to analyze the plate. The most common approach is the tension-field strut model, oriented in the direction of the tension field “a.” Plate elements with orthotropic properties oriented in the “a” direction may be used in the lateral model as a substitute for the struts. These tension struts are designed as tension members. This approach is represented by the following equation:

.

The suggested maximum height/length aspect ratio (h/L) is 1. A large height/length ratio means the vertical boundary elements’ stiffness and capacity will have more influence on the system quality. The suggested minimum length/thickness ratio is 180. Thicker plates will delay the development of tension-field action.

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Where:L = steel plate panel lengthh = steel plate panel heightw = steel plate thicknessAc, Ic = vertical boundary element memberarea and moment of inertiaAb = horizontal boundary element member area.member area


3. Boundary Elements:

The boundary elements are very important to the proper performance of SPSW systems. For boundary elements with plate walls on one side only (edge boundary elements), the boundary element should be designed based on the capacity of the steel plate wall. Thisdemand is based on the panel’s aspect ratio, the steel plate’s thickness, and the steel plate’s expected strength.

The vertical boundary elements, whether built-up or comprised of standard “W” shapes, should meet the AISC compactness criteria.

4. Hinging Sequence:

The desirable hinging sequence for the SPSW system is as follows:

1. Steel plate walls2. Coupling beams3. Horizontal boundary elements4. Vertical boundary elements

7. CONSRUCTION CONSIDERATIONS

There are several important factors that need to be considered by the engineer in order to produce good SPSW behavior and an efficient construction process.

1. SPSW Fabricated Panel Size and Details.

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SPSW panels can consist of large steel panels with low out-of-plane stiffness, which can create difficulties for stick building/erection of the system. The engineer should plan the panel segment size and details to mitigate this construction issue. Sufficient out-of-plane stiffness should be provided.

2. Careful Construction Sequence Plan.

The engineer, with assistance from the contractor, should plan the construction sequence to alleviate gravity-load induced axial compression in the steel plate panels. Axial pre-compression in the steel plate wall may delay the development of the tension-field action. One Approach to overcome this is to delay the tightening/fixing of the steel plate splice connection. This will allow shortening of the vertical elements prior to fixing the steel plate splice

3. Stability during Construction.

One of the advantages of using the SPSW system is speed of Construction. The engineer needs to make sure that the assembled system has sufficient out-of-plane stiffness during construction. The SPSW has less out-of-plane stiffness in comparison to a concrete wall.

REFERENCES

1. “Steel plate shear wall: practical design and construction” By Ignasius F. Seilie, P.E. and John D. Hooper, P.E.,

Published in The steel conference.

2. “Seismic Behavior and Design of Steel Shear Walls”

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By Abolhassan Astaneh-Asl, Ph.D., P.E. Professor Department of Civil and Environmental Engineering University of California, Berkeley.

Published in structural steel educational council.

3. “seismic Behaviour and Design of composite shear wall” By Abolhassan Astaneh-Asl, Ph.D., P.E. Professor Department of Civil and Environmental Engineering University of California, Berkeley.

Published in structural steel educational council.

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