EPSC 330 : Earthquakes and Earth Structure

Earthquake Engineering: Earthquake-resistant Structures and Testing

Phillip Salamy

Sherif Mansour

Earthquake Engineering❖ Analysis of structures

❖ Design with earthquake risk considerations

❖ Aim to increase resistivity to earthquakes

❖ Two Parts:❖ Predict consequences of high

magnitude earthquakes on structures through testing

❖ Design buildings capable of resisting earthquake damage through energy dissipating structures

Focus of Research

❖ Steel Plate Shear Wall (SPSW)

❖ advanced method of resisting strong earthquake and wind lateral loads

❖ Shake Table Test

❖ most accurate simulation method of determining structural behavior under earthquake loads

Steel Plate Shear Wall (SPSW)

❖ In the 1970’s, engineers began to research and implement SPSWs as a lateral load resistant system

❖ Sole purpose: withstand seismic activities

❖ Most buildings currently have reinforced concrete walls, however, SPSWs provide a multitude of benefits

❖ Primarily used in North America and Japan

How It Works❖ A SPSW consists of steel infill plates, two

boundary columns and horizontal beams installed throughout the full height of a structure

❖ The walls absorb the lateral forces of earthquakes and transfer the force to the foundation, dissipating the energy

❖ The framing beams are designed to withstand the gravity load without considering the plate walls

❖ In the case of the plate buckling

How It Works (cont.)❖ Steel Infill Plates

❖ Mainly designed to withstand seismic or wind loads

❖ Post-buckling behavior of these plates is advantageous to the system, by providing higher shear resistance❖ Tension field produces

diagonal brace

❖ The physical properties of steel plates are extremely suitable for resisting cyclic loads

Design Factors

❖ “a” is the inclination angle of the tension field❖ This value allows us to

compute the max shear force, V

❖ Can also compute the thickness of the panels❖ Thickness and V depend

on which story of a building

Advantages❖ Wall Thickness and Weight

❖ Compared to concrete, steel requires 10” less in thickness

❖ This results in a 2% savings in gross square footage

❖ Light weight, which results in reduced foundation and building seismic loads

❖ Easy Construction and Repair

❖ The process of constructing an all steel building is faster than concrete, which leads to a cheaper overall cost

❖ Retrofitting

❖ The small cross-section of SPSWs assist with overall design

❖ Infill plates can be replaced for a decent cost

Advantages (cont)

❖ Great energy dissipation for high risk seismic areas

❖ Ductility❖ With proper detail, these plates can experience up to 4% drift without

significant damage❖ Requires less seismic force resistance

Disadvantages❖ Initial compressive force in the

steel panels could falter with the tension-field phenomenon

❖ Must construct in a proper sequence in order to avoid this extra compression

❖ U.S. Federal Courthouse in Seattle

❖ Connection of the steel plates was done after the dead load deformation

Kobe Office Building, Japan❖ Great Hanshin Earthquake in 1995

❖ 6.9 Magnitude that resulted in 400,000 damaged buildings

❖ Building constructed in 1988 with SPSWs from the 2nd floor and above❖ No visible damage was found after

the earthquake

❖ Studies of the building post-disaster, showed that there was minimal damage

❖ Maximum drift was 1.7% on the 29th floor

❖ Local buckling of some SPSWs occurred on the 26th story

Sylmar Hospital, California❖ 1994 Northridge Earthquake

❖ 6.7 magnitude which produced the highest recorded ground acceleration at 16.7 m/s2

❖ Up to $50 billion dollars in damage❖ The building is 6 stories with SPSWs in

the upper 4 levels

❖ Most of the damage that occurred was non-structural

❖ sprinklers, flooding, TV sets❖ The high stiffness of the structure was

the main factor as to why there was minimal structural damage

Possible Defects

Shake Table

❖ 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 behaviour

❖ Most accurate method of examining actual behaviour of structures under seismic loads.

General Procedure

Components Tested on Shake Tables

❖ Anchors, Racks - non structural

❖ Columns, dampers and other structural components

❖ Frames, walls, and other substructures

❖ Full buildings and bridges

General Design of Shake Tables❖ 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)

❖ Mounting holes designed for specimen/structure

❖ Measuring devices for displacement

❖ Shake table application software (OpenSees most common)

❖ hydraulic actuators for movement of shake table

❖ Power unit

Motion Simulation of Shake Table❖ Actuators underneath the table

that simulate the complex seismic motions with varying degrees of freedom

❖ Usually 2 actuators in the x-direction, 2 in the y-direction and 4 in the z-direction

❖ Independent rotation motion

❖ Providing different wave forms to the limitations of (v, F, x, and w of system)

Examples

Shake Table Video

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

Case Study: Shake Table Testing for SPSW

❖ SPSW - high elastic stiffness, stable bearing capacity, high energy dissipation

❖ Prototype model of a standard office building with structural steel frame construction

❖ Six lateral force resisting frames❖ Earthquake response based on

2009 NEHRP seismic hazard maps.

❖ Weight of structure 1084 kips/frame

Excitation Simulation

❖ “OpenSees” Software models earthquake excitation❖ “OpenFresco” middleware transfer system

❖ Based on ground displacement, velocity and acceleration❖ 38 accelerometers

❖ 21 wire potentiometers❖ 37 linear potentiometers

Actual Specimen and Setup

Experiment Results & Findings❖ 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 increases

❖ If length of coupling beams increases: shear strength increases

❖ 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

Data Results

Shear vs. Drift

Relevance of Results

❖ Results of worst-case scenario/resonant frequency oscillations in a structure

❖ Dealing with collapse, structural damage, non-structural 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.

Summary❖ As opposed to other structures, SPSWs provide a greater

resistance to seismic activity while also requiring less space and weight

❖ Decreases in deflection, bending moment, shear force, and axial force on structures prove that SPSWs are more economical

❖ SPSWs are still a relatively new topic in terms of structures and future research is sure to improve on these systems

❖ Shake table testing is the most accurate way of simulating performance of building under seismic loads

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