Ahmed Y. Elghazouli

Bio: Ahmed Y. Elghazouli is an academic researcher from Imperial College London. The author has contributed to research in topics: Seismic analysis & Progressive collapse. The author has an hindex of 33, co-authored 185 publications receiving 4102 citations. Previous affiliations of Ahmed Y. Elghazouli include University of Edinburgh & Hunan University.

Progressive collapse of multi-storey buildings due to sudden column loss — Part I: Simplified assessment framework

Abstract: This paper proposes a novel simplified framework for progressive collapse assessment of multi-storey buildings, considering sudden column loss as a design scenario. The proposed framework offers a practical means for assessing structural robustness at various levels of structural idealisation, and importantly it takes the debate on the factors influencing robustness away from the generalities towards the quantifiable. A major feature of the new approach is its ability to accommodate simplified as well as detailed models of the nonlinear structural response, with the additional benefit of allowing incremental assessment over successive levels of structural idealisation. Three main stages are utilised in the proposed assessment framework, including the determination of the nonlinear static response, dynamic assessment using a novel simplified approach, and ductility assessment. The conceptual clarity of the proposed framework sheds considerable light on the adequacy of commonly advocated measures and indicators of structural robustness, culminating in the proposal of a single rational measure of robustness that is applicable to building structures subject to sudden column loss. The companion paper details the application of the new approach to progressive collapse assessment of real steel-framed composite multi-storey buildings, making in the process important conclusions on the inherent robustness of such structures and the adequacy of current design provisions.

Progressive collapse of multi-storey buildings due to sudden column loss—Part II: Application

Abstract: The companion paper presents the principles of a new design-oriented methodology for progressive collapse assessment of multi-storey buildings. The proposed procedure, which can be implemented at various levels of structural idealisation, determines ductility demand and supply in assessing the potential for progressive collapse initiated by instantaneous loss of a vertical support member. This paper demonstrates the applicability of the proposed approach by means of a case study, which considers sudden removal of a ground floor column in a typical steel-framed composite building. In line with current progressive collapse guidelines for buildings with a relatively simple and repetitive layout, the two principal scenarios investigated include removal of a peripheral column and a corner column. The study shows that such structures can be prone to progressive collapse, especially due to failure of the internal secondary beam support joints to safely transfer the gravity loads to the surrounding undamaged members if a flexible fin-plate joint detail is employed. The provision of additional reinforcement in the slab over the hogging moment regions can generally have a beneficial effect on both the dynamic load carrying and deformation capacities. The response can be further improved if axial restraint provided by the adjacent structure can be relied upon. The study also highlights the inability of bare-steel beams to survive column removal despite satisfaction of the code prescribed structural integrity provisions. This demonstrates that tying force requirements alone cannot always guarantee structural robustness without explicit consideration of ductility demand/supply in the support joints of the affected members, as determined by their nonlinear dynamic response.

Extremely low cycle fatigue tests on structural carbon steel and stainless steel

Abstract: Cyclic material tests in the low and extremely low cycle fatigue regime were carried out to study the properties of structural carbon steel and stainless steel. A total of 62 experiments were performed in cyclic axial and bending configurations, with strain amplitudes up to ±15%. Materials from hot-rolled carbon steel (S355J2H), cold-formed carbon steel (S235JRH) and cold-formed austenitic stainless steel (EN 1.4301 and EN 1.4307) structural sections were tested and the results were compared. The strain–life data from the axial tests were used to derive suitable Coffin–Manson parameters for the three materials; two further extremely low cycle fatigue life prediction models were also considered. The results revealed that the three materials exhibit similar strain–life relationships despite significantly different elongations at fracture measured in monotonic tensile tests. The hysteretic responses of the materials at different strain amplitudes were used to calibrate a combined isotropic/kinematic cyclic material hardening model which can be incorporated into numerical models of structural members. The stainless steel specimens displayed significantly greater levels of cyclic hardening than the corresponding carbon steel samples. A relationship between the results obtained from axial and bending test arrangements was established through consideration of energy dissipation, enabling strain–life models to be derived from either means of testing.

Cyclic testing and numerical modelling of carbon steel and stainless steel tubular bracing members

Abstract: In order to study the cyclic response of tubular bracing members of three structural materials–hot-rolled carbon steel, cold-formed carbon steel and cold-formed stainless steel–a total of 16 square and rectangular hollow section members were tested under cyclic axial loading. The load–displacement hysteretic response, compressive resistance, lateral deflection, energy dissipation and fracture life of the specimens of these three materials were investigated. In addition, finite element models, verified against the experimental results from the current study and two other research programmes, were used in conjunction with a strain-based damage prediction method to conduct parametric studies. It is shown that existing empirical expressions for predicting the buckling resistance, post-buckling compressive strength and mid-length lateral deflections can be applied to both carbon steel and stainless steel specimens. However, the relationships between member ductility and slenderness are not representative over the full slenderness range, and are not applicable to cold-formed stainless steel members. New relationships, one for each material, are proposed to take into account the inter-relationship between global slenderness and local slenderness. The tangent stiffness throughout the loading cycle, which differed between the three materials, is found to be a crucial factor in determining the resistance to local buckling and number of cycles to failure of the braces.

Experimental monotonic and cyclic behaviour of blind-bolted angle connections

Abstract: This paper deals with the experimental behaviour of blind-bolted angle connections between open beams and tubular columns. A number of connection configurations with different geometric arrangements and bolt properties are examined. The experimental set-up, connection details and material properties are first described. A detailed account of the results and observations from seventeen monotonic and cyclic connection tests is then presented, and the main behavioural aspects are discussed. The specimens include connections with top and seat angles as well as others in which web angles are also incorporated. The experimental results offer direct information on the influence of important geometric and material properties, such as angle dimensions, column face thickness, gauge length and bolt class, on the key response characteristics including stiffness, strength, energy dissipation and failure mechanism. Based on the findings, simplified approaches through which the initial stiffness and yield parameters can be estimated, are assessed. The test results also provide essential data for the future validation of detailed numerical and analytical studies which can be employed for further assessment of the response, with a view to the development of design-oriented procedures.

Properties Of Concrete

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Minimum Design Loads for Buildings and Other Structures

Abstract: Minimum Design Loads for Buildings and Other Structures provides requirements for general structural design and includes means for determining dead, live, soil, flood, wind, snow, rain, atmospheric ice, and earthquake loads, as well as their combinations, which are suitable for inclusion in building codes and other documents. This Standard, a revision of ASCE/SEI 7-05, offers a complete update and reorganization of the wind load provisions, expanding them from one chapter into six. The Standard contains new ultimate event wind maps with corresponding reductions in load factors, so that the loads are not affected, and updates the seismic loads with new risk-targeted seismic maps. The snow, live, and atmospheric icing provisions are updated as well. In addition, the Standard includes a detailed Commentary with explanatory and supplementary information designed to assist building code committees and regulatory authorities. Standard ASCE/SEI 7 is an integral part of building codes in the United States. Many of the load provisions are substantially adopted by reference in the International Building Code and the NFPA 5000 Building Construction and Safety Code. Structural engineers, architects, and those engaged in preparing and administering local building codes will find this Standard an essential reference in their practice. Note: New orders are fulfilled from the second printing, which incorporates the errata to the first printing.

Progressive collapse of multi-storey buildings due to sudden column loss — Part I: Simplified assessment framework

Abstract: This paper proposes a novel simplified framework for progressive collapse assessment of multi-storey buildings, considering sudden column loss as a design scenario. The proposed framework offers a practical means for assessing structural robustness at various levels of structural idealisation, and importantly it takes the debate on the factors influencing robustness away from the generalities towards the quantifiable. A major feature of the new approach is its ability to accommodate simplified as well as detailed models of the nonlinear structural response, with the additional benefit of allowing incremental assessment over successive levels of structural idealisation. Three main stages are utilised in the proposed assessment framework, including the determination of the nonlinear static response, dynamic assessment using a novel simplified approach, and ductility assessment. The conceptual clarity of the proposed framework sheds considerable light on the adequacy of commonly advocated measures and indicators of structural robustness, culminating in the proposal of a single rational measure of robustness that is applicable to building structures subject to sudden column loss. The companion paper details the application of the new approach to progressive collapse assessment of real steel-framed composite multi-storey buildings, making in the process important conclusions on the inherent robustness of such structures and the adequacy of current design provisions.

Ductile design of steel structures

Abstract: Chapter 1. Introduction Chapter 2. Structural Steel Chapter 3. Plastic Behavior at the Cross-Section Level Chapter 4. Concepts of Plastic Analysis Chapter 5. Systematic Methods of Plastic Analysis Chapter 6. Applications of Plastic Analysis Chapter 7. Building Code Seismic Design Philosophy Chapter 8. Design of Ductile Moment-Resisting Frames Chapter 9. Design of Ductile Concentrically Braced Frames Chapter 10. Design of Ductile Eccentrically Braced Frames Chapter 11. Design of Ductile Buckling-Restrained Braced Frames Chapter 12. Design of Ductile Steel Plate Shear Walls Chapter 13. Other Ductile Steel Energy Dissipating Systems Chapter 14. Stability and Rotation Capacity of Steel Beams Index