The growth of industrialization and the rapid expansion of densely populated urban areas have increased the risk caused by technological and man-made hazards. In particular, the accidental or ...intentional detonation of high explosives (e.g., improvised explosive devices IEDs), can cause damages to buildings and infrastructures and severe harm people. These risks can be minimized by a better planning, design, and construction, e.g., avoiding brittle construction materials, especially within the building envelope, and adopting more robust construction techniques. The study presented in the paper investigates the capacity of light steel-based wall panels to resist the effects of external explosions. The experimental results showed the ultimate capacity of the wall panels is strongly dependant on the initial design conditions and panel-to-structure fastening solution. A numerical model has been also calibrated using Etabs program.
Resilience has many components, but two are of importance when structural systems are envisaged, i.e. the capacity to resist the hazard, or robustness, and the ability to recover from the hazard. So, ...the structure may sustain structural damage, but collapse should be avoided. Moreover, the damages are repairable, such that the initial functionality is recovered.
In terms of structural mechanics, a robust structure is associated with a good balance between stiffness, strength, and plastic deformation capacity. As a result, it is expected that alternative routes are available for redistributing the loads and prevent the progressive collapse in case of a local damage. The seismic design codes in force today aim at these objectives by applying the capacity design method and using relevant admissibility criteria. However, there are exceptional situations when the earthquakes are more powerful than expected, and even the structures correctly designed can be at risk. The situation can be worsened by cascading hazards, like fire or explosion. When safety margins are exceeded, partial or global collapse can be initiated. The reliability demands of building structures at high seismic risk need to be considered to increase the resilience. One such approach is based on the so‐called Dual Steel‐Dual Frame concept, which combines steel grades and structural systems to increase the capacity of response and reduce the consequences of extreme hazards.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Extended keynote paper of Eurosteel 2021
The robustness of steel structures during severe earthquakes is largely based on the calibration of stiffness, strength and ductility. Such a robust system ...dissipates the energy by plastic deformations in the plastic members (fuses) made from mild carbon steel (MCS), while the other members remain elastic. In the case of concentrically braced frames (CBF), the fuses can be in the form of buckling‐restrained braces (BRB), while for eccentrically braced frames (EBF), the short links could take on this role. In the case of shear walls (SW), slender steel plates can be used. To avoid oversized elastic members, they can be made of high‐strength steel (HSS). Structures made from HSS and MCS are called dual steel (DS) structures. In order to ease the post‐earthquake intervention, the fuses can be detachable. Furthermore, their replacement is less costly if the structure is re‐centred using moment‐resisting frames (MRF) connected to the main dissipative system, i.e. a dual frame (DF) structure. This paper presents the concept of DS DF structures and some examples.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Multi-story buildings often use steel moment frames as lateral force resisting systems, because such systems would allow architectural flexibility, while providing the strength, stiffness, and ...ductility required to resist the gravity, wind, and seismic loads. Steel moment frames on which capacity design concepts are applied to resist earthquake induced forces, are generally considered robust structures, with adequate resistance against collapse for other extreme hazards, for example blast or impact. Starting from this point, the present paper summarizes the results of some recent studies carried out in the Department of Steel Structures and Structural Mechanics and CEMSIG Research Center from Politehnica University Timisoara, aiming to evaluate the influence of beam-to-column joints, designed to satisfy seismic design requirements, on the progressive collapse resistance of multi-story steel frame buildings.
Structural health monitoring (SHM) is a modern technique for damage identification in the existing structure. The structural stiffness, frequency, damping, and dominant mode shapes represent the ...actual operating conditions of the structure. The main principle of structural health monitoring is to identify the modal parameters from experimental results both damaged and undamaged conditions. Damage is much effective to decrease stiffness and strength of structural components and it changes dynamic behaviour and damping ratio of whole structures. Bruel & Kjaer experimental modal analysis technique is recently used for civil engineering structures for modal parameters estimation. The paper describes the initial structural health monitoring of a steel frame. The modal parameters were estimated for undamaged conditions and these results are verified and updated by the numerical FEM tool SAP2000. For the undamaged structure, mode shapes and frequencies were calibrated properly. In the second step, damaged was initiated by dismantling one element from the lower part of the frame. The estimated modal parameters were compared to the initial one. The mode shapes and frequencies are quite different for some specific mode due to damage initiation. One extra mode was created for the damaged frame due to damage initiation. The 4th mode was not found for the initial measurement because of presence of lower beam. Lower beam restraints the 4th mode and the frame behaves more flexible. Keywords: SHM, Modal parameters, FEM modelling, Damage characterization, Experimental modal analysis (EMA).
Disproportionate or progressive collapse is a phenomenon in which entire structure or large part of it collapses because of the local failure of a structure. Resistance to such progressive collapse ...depends on continuity between elements and ductility of the connections. The ductility of commonly used bolted end plate connections may depend on the T-stub component of the connection. The aim of this paper is to study the behaviour of T-stub components of beam to column end plate bolted connections under large deformation demands associated with column loss scenario. For this purpose, a parametric study is carried out to evaluate the ultimate strength and deformation capacity considering two parameters i.e. distance between the bolts and endplate thickness. Based on the experimental data, numerical model has been validated and employed in a parametric numerical study aimed at improving the response under large deformation demands. The study indicate significant role of bolts in development of catenary forces since the ultimate tensile capacity of T-stub after undergoing large deformation in a ductile failure mode was controlled by the failure of the bolts. Parametric study reveals much higher bolt force in comparison with displacement controlled induced axial force in the T-stub indicating failure of the bolts at much lower applied axial force.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The identification and consideration of various potential hazards significantly reduce the accidents in the industrial locations where specific operations with explosive materials take place. The ...purpose of this study was to assess the effects generated by external explosions produced near an experimental steel frame building model. The novelty of the paper is the combination of experimental results on site with data from specialised databases of accidental explosions. These data were integrated using computer modelling to evaluate the risk associated with different hazardous situations (shockwave propagation, spreading of debris), and the effects on the location. The numerical simulations were performed using IMESAFR software, which is a quantitative risk assessment tool and can be used to calculate risk to personnel from commercial explosives facilities and operations. The results of the simulations were used to design the perimeter security within the site and the placement of the experimental model, considering the maximum expected blast charge. Considering the limited space available on site, the results of the simulations were very valuable and confirmed the tests that were already planned can be performed without any risk for personnel, nearby buildings and facilities.
•Four types of seismic moment connections tested under column loss scenario.•Two full strength connections and two partial strength connections.•Finite element models validated against experimental ...data.•Three connections experienced large deflections prior to failure.•Partial strength connection requires strengthening to improve deformation capacity.
The beam-to-column connections of moment-resisting steel frames should exhibit capacities that allow them to transfer the forces that develop under normally expected loading conditions. However, when a column is lost owing to accidental loading, these conditions change, and the forces are redistributed to the adjacent beams and columns. In such cases, the connections must be capable of resisting the combined axial and flexural loads and allow for the redistribution of the loads, so that progressive collapse development is prevented. In this study, we investigated the performances of four types of beam-to-column connections, namely, the welded cover plate flange connection (CWP), the haunch end plate bolted connection (EPH), the reduced beam section welded connection (RBS), and the unstiffened extended end plate bolted connection (EP), against progressive collapse. Two span frames were constructed and tested under a central column removal scenario until failure. The results from the experimental tests were used to validate finite element models. The CWP, EPH, and RBS specimens showed good ductility, with the catenary action making a significant contribution to the ultimate load resistance. Further, the ultimate rotations of the beams were greater than the deformation limit given in the latest Unified Facilities Criteria guidelines for design of buildings to resist progressive collapse. Specimen EP showed the lowest ductility and ultimate load resistance, with the bolts in the rows under tension fracturing before the catenary action could develop. Further, the failure mode for specimen EP indicated that bolt strengthening is necessary for improving its progressive collapse resistance.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In steel frame buildings the role of the beam-to-column connection is crucial for assuring structural integrity, and due to their complexity and non-linear behaviour, the bolted configurations of ...this type of connection are usually the most vulnerable elements of a building. In order to assess the behaviour of a bolted steel connection, the simplified model of the equivalent T-stub is used. Based on previous experimental studies on a parametric set of T-stubs, the aim of this study is to optimise a numerical model in order to validate the experimental data and produce a fully calibrated finite element model,created with Abaqus/Explicit FE software package. To model properly the nonlinear behaviour of the component, an analysis of the properties of the model was conducted regarding the finite elements properties, analysis properties and discretization. The solid finite element properties considered were such as
the number of nodes, integration, contact and true stress-strain material definition, including damage criteria. In this context, the assembly was subjected to a transient quasi-static explicit FE analysis using mass-scaling features. The results are expressed by comparison of Force-displacement curves obtain via numerical analysis and experimental testing.
•Redistribution capacity and development of catenary action in case of column loss were assessed experimentally.•Robust moment connections allow development of catenary forces in beams and improve ...robustness.•Two-way frame system enhances redistribution capacity over planar systems as loading demand on each element reduces.•Applied element method was used to validate numerical model.
Multistory steel frames are expected to provide resistance to progressive collapse following local damage or failure caused by extreme loading events. Features like ductility and continuity provide more deformation capacity and redistribution of loads so that the structure can bridge over damaged elements. Special measures should be taken to ensure that the connections can withstand the extreme loading and deformation demands arising from the occurrence of local failure. In addition, two-way frames will enhance the progressive collapse resistance over planar systems as the loading demand on each element reduces.
In this study, we investigated the response of two-way steel frame systems under the removal of a central column. Extended end-plate bolted connections were used to join the beams to the columns. First, an experimental test was carried out, and then, a numerical model was validated using the advanced nonlinear dynamic analysis software Extreme Loading for Structures. The system was capable of developing large deformations associated with catenary response in the beams without failure of the connections. The beam ultimate rotation is larger than the deformation limit given in the codes.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
PDF
