Siavash Soroushian

Analytical Seismic Fragility Analyses of Fire Sprinkler Piping Systems with Threaded Joints

For the first time, an analytical modeling methodology is developed for fire sprinkler piping systems and used to generate seismic fragility parameters of these systems. The analytical model accounts for inelastic behavior constituents of the system, including: threaded joints, solid braces, hangers, and restrainers. The model incorporates a newly developed hysteresis model for threaded tee joints that is validated by the experimental results of several tee subassemblies. The modeling technique at the subsystem level is validated by using the experimental results of a sprinkler piping system. The methodology is used to obtain the seismic response of the fire sprinkler piping system of University of California, San Francisco Hospital under a suite of 96 artificially generated triaxial floor acceleration histories. After the component fragility parameters are obtained for the components of the system, three system-level damage states are defined, and a joint probabilistic seismic demand model is utilized to develop system fragility parameters.

Cyclic Shear Behavior of Gypsum Board-to-Steel Stud Screw Connections in Nonstructural Walls

Gypsum steel-stud partition walls are composed of light-gauge, cold-formed steel studs, and gypsum boards attached with self-drilling screws. Previous experimental studies on the seismic performance of these walls have shown widespread failure of gypsum-to-stud connections (GSCs), initiated at very low amplitude excitation. The failure of GSCs resulted in loss of strength and stiffness of the partition walls. A series of component tests has been conducted at University of Nevada, Reno to evaluate the shear force and displacement capacities of GSCs. Fastener spacing (center to center and also center to edge), loading protocol (monotonic or cyclic), and stud thickness were varied between specimens. The test data were then used to develop fragility curves for shear capacities of GSCs in terms of displacements. Additionally, a series of nonlinear GSC hinge models were proposed and validated using component experimental data.

Response of a 2-story test-bed structure for the seismic evaluation of nonstructural systems

A full-scale, two-story, two-by-one bay, steel braced-frame was subjected to a number of unidirectional ground motions using three shake tables at the UNR-NEES site. The test-bed frame was designed to study the seismic performance of nonstructural systems including steel-framed gypsum partition walls, suspended ceilings and fire sprinkler systems. The frame can be configured to perform as an elastic or inelastic system to generate large floor accelerations or large inter story drift, respectively. In this study, the dynamic performance of the linear and nonlinear test-beds was comprehensively studied. The seismic performance of nonstructural systems installed in the linear and nonlinear test-beds were assessed during extreme excitations. In addition, the dynamic interactions of the test-bed and installed nonstructural systems are investigated.

Capacity Evaluation of Suspended Ceiling Components, Part 1: Experimental Studies

The need to understand how ceiling systems perform during an earthquake is becoming increasingly important for the design or retrofit of new buildings to meet higher performance objectives. However, few studies have been conducted on suspension ceiling systems to identify where they are vulnerable. This first of two companion articles presents the results of an experimental program designed at the University of Nevada, Reno to evaluate the seismic capacity of suspended ceiling components. Forty-two monotonic and cyclic tests were performed to obtain the shear and bending capacities of ceiling joints as well as failure capacities of ceiling panels and hanger wires. The failure mechanisms observed in each of the components are described and used to develop seismic fragility curves for different suspended ceiling components.

Capacity Evaluation of Suspended Ceiling Components, Part 2: Analytical Studies

The seismic performance of a ceiling system is difficult to analytically predict due to its heterogeneous and complex details. On the other hand, lack of experimentally based analytical models for ceiling components results in over-simplified analytical models. Therefore, this second of two companion papers minimizes the gap between the complexity of ceiling systems and the weakness of previous analytical works by increasing modeling capabilities. To do so, 32 component-level analytical models are generated based on monotonic and cyclic tests of the ceiling wires, ceiling panels, and grid connections. These models are developed to capture the axial behavior of ceiling wires, the interaction between ceiling panels and sprinkler heads, and the shear and bending behavior of grid connections in both local axes. This research promotes a pathway to conduct analytical simulations of ceiling systems in conjunction with the structures.

Impact of column-to-beam strength ratio on the seismic response of steel MRFs

The strong-column/weak-beam seismic design concept in moment resisting frames is perhaps one of the least well-understood design provisions. This study is aimed at improving the understanding of the effect of column-to-beam strength ratio (CBSR) on several seismic performance measures. Through nonlinear analyses of 3-, 9-, and 20-story moment resisting frame, the impacts of CBSR on member ductility demands, maximum inter-story drifts, and floor acceleration amplifications are investigated. For each frame, the value of CBSR is varied by changing the yield strength of the material and/or by altering sizes of the columns. The probabilities of exceeding certain performance limits are investigated through fragility analyses. The single curvature bending of the columns within a story is found to be inevitable due to the participation of higher modes of vibration. Consequently, under large ground motions, the yielding of the columns is expected even for CBSRs larger than 2.0. The fragility relationships were used to calculate the design force modification factors needed for achieving a comparable probability of column yielding for different values of CBSR. The values of the yield base shear and the inter-story drifts were found to depend more on the strength of the beams than the value of CBSR. The floor acceleration amplification was found to be the least sensitive demand parameter to the CBSR.

Design of a Test-Bed Structure for Shake Table Simulation of the Seismic Performance of Nonstructural Systems

As part of the project entitled “NEESR-GC: Simulation of the Seismic Performance of Nonstructural System,” a series of system-level full-scale experiments of ceilings-piping-partition systems will be conducted at the University of Nevada, Reno NEES Site. This project is aimed at understanding the seismic response of these systems and their interaction with each other and the parent structure. A two-story, two-bay steel braced frame spanning across three biaxial shake tables was designed as a Test-Bed structure to simulate a variety of dynamic environments. After introducing the design considerations of the Test-Bed structure within this paper, the method proposed to develop the shake table drive motions is explained. To obtain the drive motion, a transfer function (TF) was formulated for a multi-support dynamic system under differential support excitation and combined with a TF previously developed for target floor acceleration of a generic structure. A suitable high-pass filter was suggested to limit exerted demands on the shake tables. 1191 Structures Congress 2011

Axial Capacity Evaluation for Typical Suspended Ceiling Joints

In recent earthquakes, the failure of nonstructural elements, including ceiling systems, has resulted in costly damage, inoperable buildings, and endangered lives. Therefore, the need to understand how ceiling systems perform during an earthquake is becoming increasingly important. However, few studies have been conducted on suspension ceiling systems to identify where they are vulnerable. A series of suspension-ceiling component experiments were designed at the University of Nevada, Reno, using interlocking grid members, including 2-ft. and 4-ft. cross tees. The test specimens were first subjected to monotonic and cyclic loading to obtain their failure capacities. Then several axial capacity fragility curves (not the seismic fragility curves of ceiling systems) were developed based on axial displacement capacities as well as strength capacities of interlocking ceiling joints in the absence of ceiling panels. Besides the experimental studies, a series of analytical models for ceiling joints were developed and validated using component experimental data.

Seismic Fragility Study of Fire Sprinkler Piping Systems with Grooved Fit Joints

AbstractA comprehensive analytical model is developed for a pressurized fire sprinkler piping system of a hospital building. A suite of ninety-six artificial triaxial floor acceleration histories is used to generate seismic fragility parameters of the sprinkler piping system. The analytical model accounts for the inelastic behavior of braces, hangers, and wire restrainers. It incorporates an experimentally validated hysteresis model developed, as part of this study, for the moment-rotation relationship of grooved fitted joints. Component fragility parameters were obtained for lateral restrainers, hangers, and pipe joints. Three system-level damage states were defined based on the level of functionality of fire sprinkler systems and severity of leakage after a seismic event and a joint probabilistic model were utilized to obtain system-level fragility parameters. Finally, the seismic fragility of fire sprinkler systems with grooved fit joints is compared to that of a piping system with threaded joints.

Analytical Simulation of the Performance of Ceiling-Sprinkler Systems in Shake Table Tests Performed on a Full-Scale 5-Story Building

A ceiling system is composed of interlocking grid members including 4-ft.-and 2ft-long cross-tees. These members are held together at each intersection by interlocking clips attached to both ends of the members. A series of component-level experiments was performed on such members. The 4-ft.- and 2-ft.-long cross-tees were subjected to tensile and compressive forces to obtain their axial strength and stiffness characteristics. Tension and compression tests were also performed on the 2-ft. and 4-ft. clips to define their strength. Finally, the behavior of the interlocked cross-tees under cyclic axial load was investigated until failure of the connection. The experimental results were used to calibrate an integrated OpenSees model of a ceiling-sprinkler assembly that was tested at the E-Defense shake table facility in 2011. A full-scale, five-story steel moment frame building was subjected to a number of biaxial and triaxial excitations. In these experiments, more than 900 ft2 of suspended ceiling with lay-in tiles was installed on the 4th and 5th floors of the building, along with 100 ft. of sprinkler piping. The results from the analytical simulation were compared to the experimental results. This research promotes the experimentally validated computer simulation of non-structural systems and establishes a modeling methodology for future studies.