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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - SustBracedMHaz (Sustainable steel braced frame for multi-hazard mitigation)

Teaser

Summary

Modern building infrastructure needs to be constructed in accordance with high sustainability and resilience standards. Sustainability in construction can be realized with demountable structures that enable change of the building geometry (adaptability) and reuse of materials and structural members at the end of the building life. Resilience can be realized with structures that can be easily repaired if damaged, so that building structure can be restored with an acceptable short, if not immediate, time after extreme loading conditions.
The goal of this project is to address these urgent societal needs by developing a novel steel frame that can simultaneously achieve the following overall objectives: (a) Sustainability in construction, (b) Enhanced progressive collapse resistance and reparability against a sudden loss of column due to bomb blast and (c) Easy inspection and repair of damage to allow rapid return to building use and occupation after strong earthquakes.
In the context of this project, a novel column base has been developed for the novel steel frame. Analytical equations have been derived for the description of the monotonic and cyclic behaviour of the column base validated by advanced nonlinear numerical models in ABAQUS. A step-by-step graphical design methodology has been derived in for the design of a column base that remains self-centering and damage-free up to a predefined design rotation. Experiments have been performed on a scaled column base for the investigation of the hysteretic behaviour of the column base. High fidelity numerical models have been built and calibrated to the experimental results. A simplified numerical model in OpenSees has been created for the column base and implemented in a Self-Centering Moment Resisting Frame (SC-MRF). Nonlinear dynamic seismic simulations have revealed that the SC-MRF when accompanied with the proposed column base can exhibit superior seismic performance in comparison to a conventional column base. The same novel SC-MRF building has been used for the investigation of the progressive collapse resistance under one or two column removal scenarios. In a first step, simplified numerical models have been created in ABAQUS for the fin-plate connections and the composite slab of the building and a detailed numerical model for the post-tensioned (PT) beam column connection. All the models have been then validated against experimental results published in scientific journals. Then, the first floor of the prototype building has been modelled in ABAQUS and subjected to one or two column removals either of the SC-MRF or of internal gravity frames. Nonlinear pushdown and dynamic analyses have been performed that proved the significant contribution of the PT beam-column connections and the composite slab to the overall progressive collapse resistance, the negligible influence of the fin-plate connections and the high robustness against the specific hazard the chosen building has possessed.

Work performed

The following have been achieved from the beginning of the project in collaboration with the Supervisor (Scientist in Charge):
(1) An extensive literature review has been performed on connections and friction materials used in friction energy dissipation devices and the progressive collapse of steel buildings.
(2) Two prototype steel buildings of 4 and 5 stories have been selected/designed for the development of the novel column base, the seismic assessment of a SC-MRF incorporating the proposed column base and the progressive collapse resistance investigations.
(3) A novel rocking and self-centering column base has been developed for enhancing the seismic performance of steel buildings. The column base incorporates four post-tensioned high strength steel bars for achieving self-centering capabilities and four friction devices for the dissipation of energy.
(4) A number of experiments was performed on a scaled column base under monotonic and cyclic loading and numerical models were built in ABAQUS to validate the experimental results.
(5) The progressive collapse resistance of a prototype steel building with SC-MRF has been investigated under one or two column removal scenarios. For that purpose, simplified numerical models have been built in ABAQUS for the description of the composite slab, the fin-plate connections and the SC-MRF. The complete ground floor was modelled in ABAQUS and the progressive collapse resistance has been studied via nonlinear pushdown and dynamic analyses.

Final results

The proposed connection details using smart friction devices and post-tensioned steel bars overcome the disadvantages of conventional connections. More specifically, these connection details can help buildings to achieve high sustainability standards by allowing deconstruction (and so, reuse of structural members and materials) and high resilience standards by avoiding damage and the associated high repair costs.
The robustness of a steel building incorporating two SC-MRFs under one or two column removal scenarios was investigated numerically via ABAQUS. Very efficient and robust numerical models, either simplified or detailed, were built to describe all the significant part of the prototype building e.g. the composite slab, the fin-plate connections and the SC-MRF. A fully detailed model of the first floor of the prototype building was built in ABAQUS to study the progressive collapse resistance in one or two column removal scenarios. The numerical analyses proved the significant contribution of the post-tensioned steel bars and the composite action of the slab to the overall progressive collapse strength of the building and showed the significant robustness these kinds of buildings can have under the specific hazard.