Manos Maragakis

Floor Accelerations in Yielding Special Moment Resisting Frame Structures

Severe damage to acceleration sensitive nonstructural components in recent earthquakes has resulted in unprecedented losses. Recent research has been aimed at increasing the understanding of acceleration demands on nonstructural components in buildings. This investigation subjects a set of four special moment resisting frame (SMRF) building models to a suite of 21 far-field ground motions using the incremental dynamic analysis procedure. Full three-dimensional models including floor slabs are used to extract both the horizontal and vertical responses. Floor acceleration response spectra are generated to assess the acceleration demands on elastic nonstructural components. Changes to the current code provisions that include the influence of structural period are proposed. An alternative design approach that directly amplifies the ground acceleration spectrum to achieve the desired floor acceleration spectrum is presented.

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.

A Methodology for the Experimental Evaluation of Seismic Pounding at Seat- Type Abutments of Horizontally Curved Bridges

Seat-type supports are normally used at bridge ends to accommodate thermal expansion and eliminate the high stresses that would otherwise be present in the superstructure when the ends are rigidly held. However, during large seismic events, there is high possibility that the joint gap between the end of the bridge and abutment backwall would close and high acceleration impact would result. It is expected that this abutment backwall pounding would significantly affect the bridge response. Yet, limited experimental research has been conducted to investigate the extent, how, and what components are affected by such effect. As a part of a Federal Highway Administration funded project, a two-fifths scale curved bridge model was constructed at University of Nevada, Reno Large Scale Structures Laboratory for shake table testing. One of the six configurations of the bridge model was designed to experimentally study the seismic performance of seat-type abutments, abutment backwall pounding, and its effect on bridge response. An abutment setup was designed to facilitate the investigation of the abutment impact accounting for the nonlinearity of the backfill soil. A compression-only device with permanent deformation was developed to represent the soil passive resistance. This paper describes the experimental setup developed to evaluate the seismic performance of seat-type abutments and characterize the interaction between the bridge superstructure, abutment backwalls, and nonlinear soil backfill.

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.

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.

Capacity Evaluation of Suspended Ceiling-Perimeter Attachments

AbstractReported frequently in recent earthquakes, failure of the ceiling perimeters in suspended ceiling systems leads to propagation of damage to the rest of the system. Therefore, the need to understand how ceiling systems perform around their perimeters during an earthquake is becoming increasingly important. In this study, a series of component-level experiments was designed at the University of Nevada, Reno to estimate the ceiling-perimeter capacities. Test specimens were constructed from cross tees and main runners, which were then connected to a portion of gypsum–stud partition wall using either pop rivets or seismic clips. The test specimens were subjected to monotonic and cyclic loading to obtain their failure capacities. Then, several fragility curves were developed for ceiling joints based on available experimental data. In addition to the experimental studies, a series of analytical models for ceiling-perimeter joints was developed and calibrated using component experimental data.

Development and Validation of a Numerical Model for Suspended-Ceiling Systems with Acoustic Tiles

AbstractNonstructural systems are responsible for the majority of national loss suffered during earthquakes, and suspended ceilings with acoustic lay-in tiles are among the most significant—and most vulnerable—of these nonstructural systems. Expensive full-scale experimental shake table tests are generally preferred over mathematical modeling techniques for simulating the seismic performance of these suspended-ceiling systems. Because of this traditional reliance on shake table testing, there is currently no experimentally validated finite-element model of suspended-ceiling systems. This paper addresses this crucial knowledge gap by introducing the first experimentally validated computer simulation of suspended-ceiling systems and by establishing a modeling methodology for future numerical studies. This study is the first to use finite-element modeling for a heterogeneous system (in this case, ceilings composed of loose components). This project aimed to develop (1) the feasibility of combining finite-ele...

Seismic Fragility Study of Fire Sprinkler Piping Systems

A numerical modeling method was developed for fire sprinkler piping systems with threaded/grooved joints and used to generate seismic fragility parameters. The model accounts for the inelastic response of grooved/threaded joints, braces, hangers, and wire restrainers. The model incorporates a nonlinear model recently developed for the cyclic moment-rotation relationship of grooved tee joints, as well as a numerical model formerly developed for threaded tee joints. The models are validated using the results of extensive experiments on tee subassemblies performed at University at Buffalo. The model is adaptable to different pipe diameter joints. A real fire sprinkler system of a hospital was simulated and its seismic response was obtained under a suite of ninety-six artificially generated tri-axial floor acceleration records. Three system damage states were defined and a combined probabilistic seismic demand model was utilized to obtain system-level fragility parameters.