Fragility Assessment of Combined Heavy Timber-Steel Bracing System Through Hybrid Simulation

Abstract

This study performs a fragility assessment of a combined heavy timber-steel friction braced framing system through hybrid testing. Hybrid simulation is an innovative testing method that combines analytical modeling with experimental testing utilizing the unique advantages that each has to offer. In a hybrid test a large portion of the structure is modeled analytically while critical structural elements, whose behaviour is expected to be highly nonlinear and thus difficult to capture analytically, are physically tested in the laboratory. In this study, one bottom storey bay of a 7 storey prototype structure is physically tested in the laboratory while the remaining lower bays and the upper 6 storeys are modeled numerically in OpenSees. One hundred and sixty five hybrid tests are performed through incremental dynamic analysis and fragility curves are developed to estimate the probability of damage at varying seismic intensities. The prototype structure is assessed at various performance levels including design and maximum credible hazard levels. The results from the hybrid test are compared with the results from the purely analytical simulation to assess the accuracy of the current finite element modeling techniques. Results show good agreement up to 2.0 percent maximum interstorey drift. The combined heavy-timber steel seismic force resisting system containing friction braces as the primary source of lateral resistance is an effective means of reducing seismic damage to this type of structure. The modeling system exhibits predictable behaviour and experimental results indicate the model is conservative.iii extend a special thanks to Josh Woods and Said Said for their countless hours of help in Carleton University's structures laboratory through the experimental program. iv 113 Research Council, 2011) limit is 2.5%. Based on the results presented, the structure had a 4% chance of reaching the collapse prevention performance category and an 87% chance of reaching the life safety performance category. Chapter 6 will compare results of the experimental IDA and it's fragility curves with these results.

Experimental and analytical fragility assessment of a combined heavy timber–steel‐braced frame through hybrid simulation

“…The design resulted in a 7‐ply SPF No1/No2 CLT slab (245 mm overall thickness) used throughout the building. Additional details on the design of the timber elements are available in Miller 32 …”

“…The resulting shear capacities of all of the GIR connections was found to be much higher than the design shear forces. Additional details on the design of the GIR connections are available in Miller 32 …”

“…The integration scheme does not require iterations and is unconditionally stable. Additional information on the numerical modeling approach used in this study is available in Miller 32 …”

“…Additional details on the design of the timber elements are available in Miller. 32 A friction brace is constructed using two steel sections connected together using a series of steel plates with slotted holes that are bolted together. The steel plates slide relative to one another creating a friction interface.…”

“…Additional details on the design of the GIR connections are available in Miller. 32 Table 1 shows the final design member sizes of the heavy timber beams, columns, and design details for the GIR connections. Additional information on the design philosophy for the timber-steel-braced frame and the capacity-based design approach for the GIR connections and timber members can be found in Gilbert and Erochko 1 and Miller.…”