Progressive Collapse Resistance of RC Beam–Slab Substructures Made with Rubberized Concrete

Abnormal loads can produce localized damage that can eventually cause progressive collapse of the whole reinforced concrete (RC) structure. This might have devastating financial repercussions and cause numerous severe casualties. Numerical simulation, using the finite element method (FEM), of the consequences of abnormal loads on buildings is thus required to avoid the significant expenses associated with testing full-scale buildings and to save time. In this paper, FEM simulations, using ABAQUS software, were employed to investigate the progressive collapse resistance of the full-scale three-dimensional (3D) beam–slab substructures, considering two concrete mixes, namely: normal concrete (NC) and rubberized concrete (RuC) which was made by incorporating crumb rubber at 20% by volume replacement for sand. The FEM accuracy and dependability were validated using available experimental test results. Concrete and steel material non-linearity were considered in the FE modelling. The numerical study is extended to include eight new models with various specifics (a set of parameters) for further understanding of progressive collapse. Results showed that slabs contribute more than a third of the load resistance, which also significantly improves the building’s progressive collapse resistance. Moreover, the performance of the RuC specimens was excellent in the catenary stage, which develops additional resilience to significant deformation to prevent or even mitigate progressive collapse

Progressive collapse resistance mechanism of RC frame structure considering reinforcement corrosion

Corrosion causes reduction in cross-sectional area of reinforcement, deterioration of mechanical properties, and degradation of bonding properties between reinforced concrete, which are the most important factors leading to the degradation of structural service performance. In order to investigate the progressive collapse mechanism of a corroded reinforced concrete frame structure, the failure modes, characteristics of the vertical displacement, and load capacity are studied using the finite element method. Based on existing experimental research, the established model is verified, and the influence of different influencing factors on the progressive collapse mechanism is analyzed. The results show that the corrosion of the reinforcement affects the yield load, peak load, and ultimate load of the reinforced concrete substructure. As the corrosion rate increases, the tensile arch action shows a particularly severe deterioration. The variation of concrete strength and the height–span ratio affects the substructure’s load-bearing capacity much more significantly than the stirrup spacing

Performance and Design of Composite Modular System with Tenon Connections for Multi-Storey Buildings

Modular building is an innovative construction method based on advanced manufacturing technologies, which is a more eco-friendly, effective, and cost-saving alternative than conventional methods. The primary objective of this thesis is to design a sufficient composite modular system for multi-storey applications and provide design recommendations based on system-level analyses under earthquakes, winds, and sudden column losses. In the course of this thesis, a numerical model is first created for an existing tenon-connected inter-module connection to investigate its effects on the building’s lateral resistance. A cohesive interface model is used to account for the weld fracture. Due to the semi-rigid connectivity, there are around 53% and 28% reductions in the yield and maximum capacity of the building, respectively. The displacement coefficient method per American guidelines FEMA-356 is then adopted to predict the maximum deformation of the modular buildings under different design seismic loads. To strengthen the modular buildings, a novel composite modular system is newly proposed, which consists of concrete-filled steel tubular columns, laminated double beams, and integrated composite slabs. The structural responses of the composite modular buildings are assessed under design wind actions per Australian Standards AS 1170.0-2. The results indicate that the proposed buildings have sufficient design capacity but insufficient deflection control. The progressive collapse analysis is performed on the buildings in sudden column loss scenarios per Unified Facilities Criteria UFC 4-023-03. The results show that alternate load paths are activated after the notional column removals, and the progressive collapse is unlikely for the scenarios under consideration. Finally, the suitable dynamic increase factors of 1.90 and 1.60 are recommended for the 4- and 12-storey modular buildings, respectively, allowing peak dynamic responses to be predicted using the static approach

Steel-concrete frames under the column loss scenario: An experimental study

Accidental events, such as impact loading or explosions, are rare events with a very low probability of occurrence. However, their effects often lead to very high human losses and economic consequences. An adequate design against these events should reduce the risk for the life of the occupancy, minimize the damage extension and enable a quick rebuilding and reuse. A structure fulfilling these requirements is ‘robust’. Different strategies can be pursued for accidental events, and among them, methods based on the residual strength or the alternate load path are frequently adopted because applicable to a vast range of structures. Adequate design strategies based on them require an in-deep knowledge of load transfer mechanisms from the damaged to the undamaged part of the structure. As to the frames, the important role of joint ductility was pointed out in recent studies. Besides, the flooring systems substantially affect the spread of the damage, but the research on this subject is still very limited. The present study focuses on steel-concrete composite frames under the column loss scenario. It aims to better understand the influence of both frame continuity and floor systems in the development of 3D membrane action. Two geometrically different 3D steel-concrete composite full-scale substructures were extracted from reference buildings and tested simulating the column collapse scenario. This paper illustrates the preparatory studies, the main features of the specimens and the outcomes of the first test. The test provided an insight in the need for an enhanced design of joints and pointed out the key features of the response of the floor system

Deterministic, probabilistic and risk-based design for progressive collapse of RC structures based on a novel method

Progressive or disproportionate collapse is a structural failure mechanism accompanied with a significant disproportion between the initiating event and the ensuing failure consequence. Facing a possible huge economic loss and even large casualties, structures must be designed with sufficient robustness. Several structural design codes and standards have presented guidelines to increase the robustness of structures. However, these guidelines are largely of deterministic nature and may not be effective, because structures involve large variation in loading, material properties, etc. These variations can lead to significant uncertainty in the degree of robustness of structures and should be dealt with in a probabilistic framework. Based on a new direct design method developed by the authors recently, this study showed that how probabilistic and risk-based design for progressive collapse can be accomplished from a case study. The method can not only help engineers quickly conduct probabilistic performance-based design of structures against progressive collapse, but also communicate with stakeholders more efficiently if adopting risk-based design strategy.This research was partially supported by National Key Research Program of China (grant number 2016YFC0701400), National Natural Science Foundation of China (grant number 51338004), and the Discovery Grant program of the Natural Science and Engineering Research Council (NSERC) Canada. The study was conducted during the first authors visiting research at Ryerson University. The funding support from the China Scholarship Council (CSC) for the first author is also gratefully acknowledged

Improving the resistance to progressive collapse of steel and composite frames

Several well publicised examples of progressive collapse have heightened concerns about the need to address robustness as a design requirement. Although research around the subject has been aimed at understanding the mechanics of progressive collapse, little work has been done on translating findings into better guidance on how to ensure adequate resistance without relying on the current prescriptive rules. Based on the Imperial College London method, which provides a soundly based analysis framework for calculating and comparing the performance of different designs, the work presented herein introduces a methodology for making realistic and effective design interventions, in order to allow designers to effectively enhance the robustness of their structure. This strategy is illustrated for both steel and composite frames and covers structures designed for both seismic and non seismic locations. Using the proposed step-by-step methodology, it is possible to redesign a simply designed composite frame in a way that it will be sufficiently robust to cope with any sudden column removal scenario. Comparison with simply increasing tying capacity reveals that the latter does not have a direct and proportional effect on the frame’s resistance and should be used within a more informed context. With the aim of performing a complementary study for moment resisting steel frames, three types of popular welded connections are modelled under progressive collapse loading conditions using the Component Method. Also, an analytical solution for the prediction of the response of irregular beam systems under sudden column loss is presented. Despite the excellent performance of most floor systems, moment frames are found vulnerable to certain column loss scenarios. Thus, these scenarios are further examined with the express purpose of identifying how the frame might best be configured so as to provide the necessary resistance. The findings show how design for seismic resistance and design to resist progressive collapse do not necessarily align and highlight which structural properties are the most important to consider in each frame type, therefore encouraging the use of the proposed redesigning methodology, which is capable of effectively remediating robustness by efficiently addressing localised weaknesses.Open Acces

MECHANICAL PERFORMANCE OF STRUCTURAL SYSTEMS WITH MISSING MEMBERS: FROM BUILDINGS TO ARCHITECTED MATERIALS

Structural systems are potentially subjected to damage initiating scenarios throughout the course of their service time. Depending on the nature and extent of the damaging event, they may experience significant reduction or even complete loss of their mechanical performance. This dissertation delves into the mechanics of structural systems under the notion of missing members from their domain, investigating types of structural systems: a) multi-story steel framed buildings, and b) materials with a truss-lattice microstructure. Part I of the dissertation investigates the performance of multi-story steel framed buildings under a column removal scenario, developing an analytical framework for their quasi-static robustness assessment. Two system-failure modes are taken into consideration: i) a yielding-type mechanism, where damage propagates as a series of beam plastic hinges or gravity connection failures, and ii) a stability-related mechanism, where a building column fails due to buckling. Validated against finite element results, this study demonstrates the capability of the method to assess the key features of the building performance such as the dominant collapse mode, the system capacity and the damage propagation path. Most importantly, it highlights that the governing mode is strongly dependent on the location of the initial damage scenario, emphasizing therefore the necessity for system-level approaches to identify correctly the building structural response. Part II of the dissertation draws attention to the emerging class of architected materials with a truss-lattice microstructure, and performs a detailed study on the impact of missing struts to their elastic mechanical behavior. Considering a list of truss-lattice topologies with varying coordination numbers (connectivity) and accounting for a series of defect scenarios, this work identifies the effect of the various topological parameters that govern the degradation rates of the elastic constants, such as the lattice connectivity, anisotropy, and interrelation of the pristine elastic constants. This investigation is supported by numerical (finite element modeling), experimental (two-photon lithography) and analytical (elastic micromechanical models) approaches. The results revealed that the behavior of periodic imperfect truss-lattices with coordination number Z≥12 is almost indistinguishable from homogeneous materials, and demonstrated a clear trajectory between the topology coordination number and the least deleterious defect arrangement

Developing OpenSees software framework for modelling structures in fire

Fire following an earthquake (FFE) is a hazard that is not usually accounted for in either earthquake or fire resistant design of structures. There have however been many instances in the past of FFE events causing even greater damage and even loss of life than the original earthquake. The potential damage associate with this hazard is increasing considerably with increasing urbanisation in seismically vulnerable regions. It is reasonable for users to expect that structures should maintain their integrity for a long enough period in an FFE event allowing emergency crews to assist the most vulnerable occupants to evacuate the building safely. Because of the lack of regulatory requirements there is naturally very little research on the response of structural frames under FFE events so far, but given the reasons discussed earlier, it is clearly a matter of increasing importance that engineers should develop a better understanding of the behaviour of seismically damaged structural frames in fire. This thesis project was fortunate to have occurred at a time when a set of full-scale fire tests were taking place at IIT Roorkee in India, in collaboration with the University of Edinburgh to address exactly this topic. This thesis research was undertaken to model these experiments (to determine the fire resistance of a reinforced concrete frame first subjected to simulated seismic damage). The open source software framework OpenSees was chosen for the modelling work as it was considered to be the best software tool for modelling structures under earthquake loading. The first part of this thesis reports the development work done on OpenSees for adding thermomechanical analysis modules to enable the modelling of FFE events using this software framework. The code developed for OpenSees has been allowed the introduction of features not available in commercial software such as ABAQUS. Many new classes were developed, such as ThermalAction, ThermalElement, ThermalSeciton, TheramalMaterial, etc. The newly developed code was tested using a number of benchmark problems and modelling of real fire experiments on steel and composite framed structures. The results from these tests showed that the new developments were successful. The second part of the thesis describes the modelling of the reinforced concrete (RC) frame tested at IIT Roorkee, which was first subjected to cyclic displacement loading (to introduce damage in the frame similar to that of a seismic event) and then to a one hour kerosene fire. The modelling was first used to provide predictions of the performance of the test frame under the proposed loading, to fine tune the design of the experiment. The modelling subsequent to the tests was gradually improved to achieve better comparisons with the test results and to develop a detailed understanding of the behaviour of seismically damaged RC frames in fire, which was also compared to the behaviour in fire of undamaged frames