What is a Steel Plate Shear Wall (SPSW) and How Does It Work?

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1 Earthquake Engineering Abstract Introduction Earthquake engineering is the branch of engineering that focuses on the design and analysis of structures with earthquake risk concerns. The main goal of earthquake engineering is to enhance the structure s resistance to seismic loads and oscillations. Components of earthquake engineering include examining data from past earthquakes in history, theoretical predictions, computer simulations such as non-linear finite-element stress analysis, testing structures, and designing more resistive structures through the optimizing of materials and geometries. The focus of this presentation is split into two sections: a construction method and a testing method. The design construction method is the implementation of steel plate shear walls (SPSW), which is one of the most advanced methods of resisting strong earthquakes and energy dissipation in buildings. The testing method is the shake table test which is currently the most accurate means of predicting the behavior of the structure under earthquake loads. What is a Steel Plate Shear Wall (SPSW) and How Does It Work? A SPSW is a lateral load resistant system designed in the 1970s with the sole purpose of withstanding seismic activities. This system consists of steel infill plates, two boundary columns and horizontal beams installed throughout the full height of a structure as seen in Figure 1.

2 These systems absorb the lateral forces of earthquakes and transfer this force to the foundations of the building, therefore dissipating the energy. As for the design of the SPSW, all of the framing beams, the horizontal and vertical, are particularly designed to withstand the total gravity load without considering the plate walls. This is done in case the plate buckles and cannot help support the load. The infill panels are designed to withstand the seismic or wind loads. They experience a post buckling behavior that provides a higher shear resistance. As the plate buckles, a tension field is created, as seen in Figure 2, that resists the lateral loads. How are SPSWs Designed? The equation in Figure 3 allows us to calculate the inclination angle,, of the tension field. From there, we can calculate the maximum allowable shear force and thickness based on the different story levels of a building or structure. A sample of a SPSW under shear is shown in Figure 4.

3 What are the Advantages and Disadvantages of SPSWs? Advantages: SPSWs require about 10 less thickness than reinforced concrete shear walls. This helps save 2% gross square footage. Additionally, this would lead to less weight required of the overall structure SPSW construction requires less time; therefore, there is a reduction in total cost of a project. Retrofitting of SPSWs is much easier and faster than concrete methods The ductility of steel allows for a 4% drift without damage to the structure. Also, the stiffness leads to a decrease in deflection compared to concrete shear walls. Disadvantages: The construction sequence of SPSWs needs to be highlighted, as an improper order could lead to a high initial compressive force in the plates. This excess force could falter with the tension-field phenomenon. Case Study: Kobe City Hall, Japan In 1995 a 6.9 magnitude earthquake known as the Great Hanshin hit Kobe, Japan. This earthquake resulted in the damage of about 400,000 building. The building seen in Figure 5 is the city hall which was constructed in 1988 using SPSWs from the 2nd floor and up. It was reported that after the earthquake, there was no visible damage present. Studies of the building post-earthquake showed that there was minimal damage. They found that the maximum drift experienced was 1.7% and that local buckling of some SPSWs occurred on the 26th floor.

4 Case study: Sylmar Hospital, California A 6.7 mag earthquake hit a region of Los Angeles, California. This earthquake recorded one of the fastest ground acceleration at 16.7 m/s2 and resulted in up to 50 billion dollars in damage. This hospital, seen in Figure 6, is a 6-story building with the upper 4 floors having SPSWs installed. Most of the damage that occurred was non-structural such as damage to the sprinkler units causing flooding, and TV sets that were bolted to walls broke off. There was minimal structural damage due to the high stiffness of the structure. Shake Table Testing: Test the response of structures to earthquakes of different magnitudes Models the vibrations of a real seismic event Video recordings and data collection through transducers used to analyze structure behavior Most accurate method of examining actual behavior of structures under seismic loads.

5 General Design of Shake Tables: Mounting holes designed for specimen/structure Measuring devices for displacement Shake table application software (OpenSees most common) hydraulic actuators for movement of shake table (Figure 8) Power unit Stiff table - usually concrete Designed for high stiffness and high natural frequency Controller for commanding movement on shake table including rotation, translation about 3 principal axes. Pressurized Air chamber below shaking table PEER Earthquake Shaking Table is the largest and oldest (1972) Advantages of Shake Tables: Most accurate/realistic force consideration (inertial and damping) and dynamic effects on a structure undergoing seismic activity No loading devices required Easiest way of simulating ground motion effects on a structure

6 Summary of Findings from Testing SPSW: key insight into seismic response of SPSW system SPSW can minimize the damage of the gravity frame components of the lateral force resisting system If cross section is increased: shear strength and degree of coupling increase If length of coupling beams increases: shear strength increases and degree of coupling decrease Strength degradation happens faster in small length, large cross section coupling beams Increasing length and cross section area decreases rotation but risks failure in connection Relevance of Results: Results of worst-case scenario/resonant frequency oscillations in a structure Dealing with collapse, structural damage, nonstructural damage and internal damage in buildings Data collection can be used in the aid of the design process considering areas of maximum stress concentration and displacement. Sources: [1] Story Reinforced Concrete Building Tested on the NEES-UCSD Shake Table, J. Struct. Eng., vol. 144, no. 3, p , Mar [2] S. Brown, SEISMIC ANALYSIS AND SHAKE TABLE MODELING: USING A SHAKE TABLE FOR BUILDING ANALYSIS, [3] M. Ge, J. Hao, J. Yu, P. Yan, and S. Xu, Shaking table test of buckling-restrained steel plate shear walls, J. Constr. Steel Res., vol. 137, pp , Oct [4] D. M. Dowden and M. Bruneau, Dynamic Shake-Table Testing and Analytical Investigation of Self-Centering Steel Plate Shear Walls, J. Struct. Eng., vol. 142, no. 10, p , Oct [5] International Association for Earthquake Engineering. and International Association for Structural Control., Earthquake engineering & structural dynamics. John Wiley & Sons. [6] U. Ashish and R. Harshalata, Effect of Steel Plate Shear Wall on Behavior of Structure, Int. J. Civ. Eng. Res., vol. 5, no. 3, pp , 2014.

7 [7] I. F. Seilie and J. D. Hooper, Steel Plate Shear Walls: Practical Design and Construction. [8] M. Bruneau, J. Berman, and J. W. Berman, STEEL PLATE SHEAR WALL BUILDINGS: DESIGN REQUIREMENTS AND RESEARCH for the development of Comprehensive Specifications for the Seismic Design of Bridges, and BSSC TS6 Subcommittee on Steel Structures for the 2003 Edition of the NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Others Structures. [9] Astaneh, Abolhassan. Seismic Behavior and Design of Steel Plate Shear Walls, Structural Steel Educational Council Steel Tips. January [10] Thorburn J.L., Kulak G.L., and Montgomery C.J. (1983). Analysis of steel plate shear walls, Structural Engineering Report No.107, Department of Civil Engineering, The University of Alberta Edmonton, Alberta, pp [11] A. Pavir and B. Shekastehband, Hysteretic behavior of coupled steel plate shear walls, J. Constr. Steel Res., vol. 133, pp , Jun