STR-863: DEVELOPMENT OF A NOVEL REPLACEABLE CONNECTION FOR SEISMICALLY DESIGNED STEEL CONCENTRICALLY BRACED FRAMES

There is increasing demand, from both engineers and their clients, for structures that can be rapidly returned to occupancy following an earthquake, while also maintaining or reducing initial costs. One possible way towards this goal is to ensure that seismic damage occurs only within elements that can be removed and replaced following a damaging earthquake. For concentrically braced frames that use hollow structural sections, the current design practice requires field welding of the brace to the gusset in a way that causes the brace to buckle out-of-plane. In the event of a damaging earthquake, the out-of-plane brace buckling may damage both the gusset plate and also any adjacent exterior cladding. The plate cannot be easily replaced, resulting in expensive and time-consuming repairs, and the damaged cladding could endanger the lives of people evacuating the building and of other pedestrians. This paper discusses the development of an alternative connection that can be bolted into place and that confines damage to replaceable components. The proposed connection is expected to result in reduced erection costs and be easier to repair following a major earthquake. Moreover, the new connection causes buckling to occur in plane, preventing dangerous damage to the cladding. Potential challenges in the design of such a connection are discussed and evaluated, and a finite element model that was created to confirm the performance of the proposed connection is also introduced. Finally, future areas of research and development of the connection are identified

STR-833: EVALUATION OF THE CONTRIBUTION OF PANEL ZONES TO THE GLOBAL PERFORMANCE OF MOMENT RESISTING FRAMES UNDER SEISMIC LOAD

Before the 1994 Northridge Earthquake, the seismic design strategy for moment resisting frames considered the yielding of the panel zone when calculating the required level of ductility. Following the unacceptable performance of conventional moment resisting frame (MRF) connection details during the Northridge seismic event, prequalified connections were developed to concentrate beam yielding away from the column face, preserving the connection. With these new connection strategies, the panel zone deformation may not contribute as significantly to the overall behaviour of an MRF. Therefore, considering the increased use of advanced dynamic modeling techniques, it is important for both designers and researchers to know what level of modelling detail is required to properly capture the behaviour of an MRF. This paper examines the influence of the panel zone model on the global performance of a moment resisting frame. The nine-storey SAC building is used as a model to evaluate the influence of this variation. The beam-to-column connections use reduced beam sections and are modeled with OpenSees using nonlinear elements that that capture cyclic deterioration. In one case, the panel zones are modelled as rigid offsets with no shear yielding. In the other case, the panel zones are modeled using a rotational spring box, in which rigid links are arranged in a rectangle and connected at the four corners by three pins and one nonlinear spring that captures the shear distortion in the panel zone. An Incremental Dynamic Analysis with 7 ground motions is conducted to determine the differences in global performance. The more refined panel zone model results in a longer first mode period and less energy dissipation in the plastic hinges of the beams. However, the difference in engineering demand parameters at design level events is minimal and may not justify the increase in computational requirements unless collapse assessment is desired

STR-813: FRAGILITY OF LOW-RISE CONTROLLED ROCKING STEEL BRACED FRAMES WITH DIFFERENT BASE ROCKING JOINTS

Controlled rocking steel braced frames (CRSBFs) are resilient seismic force resisting systems that can self-centre the structure and prevent structural damage during design-level earthquakes. Energy dissipation may be provided to limit peak displacements, while post-tensioning provides self-centering after rocking. Previous studies have shown that designing energy dissipation and the post-tensioning components in CRSBFs using a response modification factor of R = 8 is sufficient to prevent collapse of structures during earthquakes higher than the design level. However, designers have unique control over the hysteretic behaviour of the system, even after the response modification factor is selected. Additionally, recent studies have suggested that CRSBFs can be designed using higher response modification factors without a significant reduction in performance. This paper examines how the design of the post-tensioning and energy dissipation components comprising the base rocking joint influences the collapse performance of a three-storey CRSBF using the results of ten incremental dynamic analyses (IDA). Ten different base rocking joints were designed for the frame using different response modification factors, energy dissipation parameters, and post-tensioning parameters. A suite of 44 ground motions was selected and scaled until collapse occurred in at least 50% of the cases, and collapse fragility curves were generated using the truncated IDA curves. The results show that the same CRSBF can have different collapse performances, depending on the parameters selected to design the base rocking joint. However, nine of the ten base rocking joints provided an acceptably low probability of collapse based on the implemented methodology

STR-850: NUMERICAL MODELLING OF REINFORCED CONCRETE BLOCK STRUCTURAL WALL BUILDINGS UNDER SEISMIC LOADING

With the recent shift of design code developers’ focus from component- to system-level assessment of seismic force resisting systems, there is a need to numerically assess the performance of whole buildings. However, reinforced concrete block structural wall buildings are complex structural systems composed of materials with nonlinear and heterogeneous properties, which makes the numerical investigation challenging, especially when seismic behavior is considered. Most previous numerical models of reinforced concrete block walls have considered individual components, rather than the complete building system, and have used relatively complex micro-models. In this paper, OpenSees (Open System for Earthquake Engineering Simulation) is used to create macro non-linear models to simulate the response of two different buildings under unidirectional cyclic loading that represents earthquake effects. The models are created in such a way as to balance the desire for accuracy with the desire for relatively simple models that can be defined using only the geometry and actual material properties, and that are not excessively demanding computationally. Detailed validation of the models is conducted to compare the hysteretic behaviour of the numerical models with available experimental test results on reinforced concrete block structural wall buildings. This paper demonstrates that simple models can, with proper calibration, capture the cyclic response, including energy dissipation and degradation of strength, very well. In this way, this study significantly enhances the database of validated numerical models for reinforced masonry shear wall buildings