E. “Manos” Maragakis

Experimental and Analytical Studies of Hospital Piping Assemblies Subjected to Seismic Loading

The seismic characteristics of welded and threaded hospital piping assemblies were investigated with and without seismic restrainers under various intensities of seismic loading using a biaxial shake table. Experimental results showed that the restrainers limited the displacements; however, they did not reduce the acceleration responses. No leakage was detected in the welded assembly up to a drift ratio of 4.3%; however, threaded piping suffered minor leaks at a drift ratio of 2.2% and experienced connection failure at a drift ratio of 4.3%. A simplified computational model was developed and calibrated with experimental data using SAP2000. The effective stiffness of the seismic restrainers was determined to be 10% of full stiffness due to their initial slack. The analyses showed that the dynamic response of the piping system as braced in these experiments with similar boundary conditions was predominantly kinematic with minimal inertial effects.

Effects of the hinge restrainers on the response of the aptos creek bridge during the 1989 Loma Prieta Earthquake

This paper presents the results of a study for the effects of the cable restrainers on the nonlinear seismic response of the Aptos Creek Bridge during the 1989 Loma Prieta earthquake. The earthquake analyses focus on the relative displacements of the hinge, the absolute displacements of the bridge, the restrainer force levels, the shear key and the shear pipe forces, the hinge impact, and the abutment and pile forces in both the longitudinal and the transverse directions. At the estimated earthquake excitation levels at the bridge site, it was found that the restrainers did not play a major role on the overall structural response. However, at higher acceleration levels they contributed significantly to the reduction of displacement and force responses.

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.

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.

Capacity Evaluation of Typical Stud-Track Screw Connections in Nonstructural Walls

A series of component-level experiments have been conducted aiming to evaluate the force and displacement capacities of typical stud-track screw connections (STCs) in steel-framed partition walls. The variables considered in these experiments included screw-edge distances, loading protocols (monotonic or cyclic), and stud and track thicknesses. The experimental data was then utilized to develop different capacity fragility curves for STCs in terms of displacements. A series of analytical STC hinge models were also proposed and validated using this data. The hinge models can be adopted in future studies to develop a comprehensive analytical model for a typical partition wall assembly.

Seismic fragility study of displacement demand on fire sprinkler piping systems

Seismic damage to fire sprinkler piping systems is not only caused by inertial forces or interstory drifts, but also by impact with surrounding objects. The collision of constituents of piping systems with nearby objects increases the chance of damage to the piping itself and to adjacent objects. In this study, the probability of seismic damage to fire sprinkler systems due to impact is quantified by obtaining seismic fragility parameters for large diameter pipes passing through walls and floors, as well as small diameter pipes that typically interact with suspended ceilings. The results of two shaking table experiments conducted at the University of Nevada, Reno and E-Defense test facility, and a high-fidelity numerical model of a hospital piping system are used to evaluate the displacement demands. Piping interaction fragility curves are generated based on clearances between adjacent objects and pipes. The probability of piping interactions and damage to piping systems subjected to different levels of peak floor acceleration is compared for different clearances. It is found that the probability of damage due to impact is comparable with the probability of exceeding other limit states, like the leakage in fittings, when a 1 in or 2 in gap is provided around large and small diameter pipes, respectively.

Experimental Fragility Analysis of Pressurized Fire Sprinkler Piping Systems

The seismic performance of nonstructural components, including pressurized fire sprinkler systems, plays a significant role during and after an earthquake. A series of full-scale system-level experiments was conducted at the University of Nevada, Reno Network for Earthquake Engineering Simulation site in order to evaluate the seismic performance of integrated ceiling-piping-partition systems. In this study, the performance of fire sprinkler piping systems were evaluated through several design variables. Processing of experimental data led to the calculation of acceleration amplification factors and development of fragility functions. Results show that 50 mm (2.0 in) diameter pipes have the greatest failure probability when evaluating pipe joint rotations.