No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Collapse prevention design criteria for moment connections in multi-story steel frames under extreme actions
Abstract
The paper investigates the role of beam-to-column connections in mitigation the progressive collapse of multi-story steel frame buildings in case of column loss. On this purpose, a set of moment frames with different beam-to-column connections is designed following seismic design criteria for highly dissipative structures to resist seismic actions. Applied Element Method through nonlinear dynamic analyses is applied to predict the structural response, after the loss of one or more columns. The model was calibrated to match experimental data from full scale tests on bolted end plate connections under bending moment and different levels of tensile axial force.
... presents the experimental set-up. The calibration of the model is detailed in [126]. Based on these tests, a numerical model was constructed, using the same loading principles, boundary conditions, and material properties. ...
... Beam-to-column connections subjected to bending moment and axial force a) Moment-rotation curves b) Bending moment -axial force interaction Figure 3.11. Calibrated model versus experimental data [126] For the evaluation of the frame behavior in case of column loss, with the development of catenary action and influence of progressive tension axial force on the connections and elements moment capacity, another set of experimental data, obtained by J.-P. Jaspart and J.-F. ...
... Tension axial forces appear only for scenarios that can develop a catenary action (A3, B2, A23). a) structure with rigid connections (FS) b) structure with semi-rigid connections (PS) Figure 3.18 Bending moment vs. rotation at maximum vertical displacement [structure with rigid connections (FS)b) structure with semi-rigid connections (PS)Figure 3.19 Axial force vs. vertical displacement[126] ...
Buildings, like other components of the built infrastructure, should be designed and constructed to resist all actions that may occur during the service life. When the actions are caused by extreme hazards, such as explosion or impact, the structural integrity should be also maintained by avoiding or limiting the damage. Depending on the type of structural system and class of importance, specific requirements should be met in order to ensure structural integrity. In the case of framed buildings, one such requirement is that after the notional removal of each supporting column (and each beam supporting a column), the building remains stable and any local damage does not exceed a certain acceptable limit. This requirement can be achieved by several means, but a combination of strength, ductility and continuity of the structural system is likely to provide a high level of protection and safety against extreme hazards. Steel frames are widely used for multi-storey buildings, offering the strength, stiffness, and ductility that are required to resist the effects of gravity, wind, or seismic loads. Considered to produce robust structures, the seismic design philosophy has been seen as appropriate for controlling the collapse of structures also subjected to other types of extreme hazards. However, there are specific issues that should be taken into account in order to forestall the localized failures, particularly of columns.
The thesis focuses on the evaluation of the structural response of steel frame buildings following extreme actions that are prone to induce local damages in members or their connections. Extensive experimental and numerical studies were used in order to identify the critical points and to find the structural issues that are
required for containing the damage and preventing collapse propagation. Four types of beam-to-column joints, which cover most of the joints used in current practice, have been investigated experimentally, and the data was used in order to validate advanced numerical models. The findings indicated that catenary action substantially improves the capacity of moment resisting frames to resist column loss, but increases the vulnerability of the connection due to the high level of axial force. The results showed that bolted connections could fail without allowing for load redistribution if not designed for these special loading conditions. The composite action of the slab increases stiffness, yield capacity, and ultimate force but decreases ductility.
Parametric studies were performed so as to improve the ultimate capacity of joints and, implicitly, the global performance of steel frame building structures in the event of accidental loss of a column, without affecting the seismic performance and design concepts. Based on calibrated numerical models, an analysis procedure was developed for evaluating the performance of full-scale structures to different column loss scenarios considering dynamic effects and realistic loading patterns. Moreover, a design procedure was proposed for verification of the capacity of beam-to-column connections to resist progressive collapse, including design recommendations for each connection configuration.
... The structure was tested by physically removing four first-story columns and results were compared to numerical results obtained using twodimensional as well as three-dimensional models. Dubina et al. [10] investigated the role of beam-to-column connections in mitigation the progressive collapse of multi-story steel frame buildings in case of column loss. The numerical model was calibrated to match experimental data from full scale tests on bolted end plate connections under bending moment and different levels of tensile axial force. ...
Capacity of multi-storey steel frame buildings to resist extreme loading may depend on the performance of beam-to-column connections. If catenary action forms, this results in large axial force demands in beams and therefore it is necessary to take into account the interaction between bending and tension for the design of connections. The paper investigates the capacity of different types of beam-to-column connections to resists large axial forces after undergoing large rotations. On this purpose, four types of beam-to-column connections are designed following seismic design criteria for highly dissipative structures to resist seismic actions. Applied Element Method through nonlinear dynamic analyses is applied to predict the structural response, after the loss of one or two columns.
... Tests performed by Gong [4] on double-angle connections confirmed that the ductile behaviour required for the development of catenary action should be assured by robustness design of the connection in accordance with the capacity design. Dubina et al. [5] also investigated the role of beam-to-column joints in mitigating the progressive collapse of multi-story steel frame buildings in case of column loss. Experimental and numerical tests on connection under quasi-static and dynamic loading performed by Rahbari et all [6] showed that the failure mode of web cleat connections is not influenced by the loading rate due to the flexibility of the connection. ...
Resistance to progressive collapse under extreme loading is a measure of the structural robustness, and relies primarily on resistance of key elements, continuity between elements and ductility of elements and their connections. In case some hazards occur simultaneously or consecutively in a very short period of time, e.g. fire after explosion or impact, the capacity of the members and connections can be exceeded and this can initiate the progressive collapse of the structure. The paper presents the results of a research program that focused on the ultimate capacity of connection macro-components under large deformation demands and different loading rates. The specimens were extracted from extended end plate bolted beam-to-column connections with different strength and stiffness ratios to the beams.
... The structure was tested by physically removing four first-story columns and results were compared to numerical results obtained using two-dimensional as well as three-dimensional models. Dubina et al. [5] also investigated the role of beam-to-column joints in mitigating the progressive collapse of multi-story steel frame buildings in case of column loss. Numerical models were validated using experimental data from full scale tests on bolted end plate connections under bending moments and different levels of tensile axial forces (Fig. 1). ...
Capacity of multi-storey steel frame buildings to resist extreme loading may depend on the performance of beam-to-column joints to provide continuity across the damaged area, and thus to allow the development of alternate loads paths (AP). It is of interest to study the capacity of actual design procedures to provide enough robustness for connections under extreme loading conditions ([1], [2]). Bolted end plate connections are widely used in the steel frame constructions. The T-stub, which is the basic component of such connections, has been extensively applied to model the tension zone that constitutes the most relevant source of deformability [3], [4], [5]. Preliminary FEM analysis [6] indicated that the ultimate capacity increases very much with the development of the catenary action, but this imposes large deformation demands on connections (see Fig. 1).
The following typologies have been selected for the experimental program: T-10-16-100; T-10-16-120; T-10-16-140; T-12-16-100; T-12-16-120; T-12-16-140 (Fig. 3). First letter represent the T-stub, second term represents the thickness of the end plate, followed by the diameter of the bolt and then the distance between the bolts, in mm. Specimens have been tested at low and high strain rate (0.05mm/sec and 10mm/sec respectively). The steel grades were S235 for flanges, S355 for webs and 10.9 for bolts. Fillet weld with a throat thickness, aw = 7mm was used to connect the web and the flange. Fig. 3 presents the force-displacement curves. There is a small influence of the loading rate, both in terms of ultimate resistance and deformation capacity. The failure is ultimately attained due to the fracture of the bolts, see Fig. 4.a.
When the distance between bolt rows increases from 100 to 120 mm, there is a reduction of the resistance, but the deformation capacity increases. When bolt row distance is increased to 140 mm, the deformation capacity increases without a reduction of the resistance. No failure of the welding has been observed. A numerical analysis program has been also developed using ABAQUS computer program to validate the numerical models for T-stub components. It can be seen the FE response follows with high accuracy the actual behavior of the specimen (Fig. 4.b).
Today, blast is a threat to all buildings in urban centers and residential areas. The blast inside or near the building, it could lead to sudden damage to building frames. The analysis and design of structures under explosive loads requires an accurate understanding of the dynamic response of members and structural systems under this loading. Today, the use of steel plate shear walls as an efficient lateral load system is being considered to increase the lateral strength and stiffness of buildings against lateral loads in concrete and steel structures. The results of experiments on steel plate shear walls indicate high stiffness, adequate strength, proper ductility and high energy dissipation under cyclic loads. In this study, a blast loading was exerted inside the plate in the steel structures with steel plate shear wall and moment frame with 6 story in the finite element ABAQUS software two-dimensionally and the occurance possibility of progressive collapse had been examined and compared. The results of this study indicated that in the case of a blast inside the plate, the steel plate shear wall had a suitable performance in comparison to the moment frame and the progressive collapse was limited, while in the case of blast outside of the plate due to the explosion wave, the moment frame had better behavior.
The presented work describes design model of end plate joints loaded by combination of bending moment and normal force. Two sets of tests were performed to check the prediction -tests at University in Coimbra and tests prepared at Czech Technical University in Prague. The procedure for the interaction is already available for base plates. The paper presents application of this model to beam-to-column connections and beam splices and verification of the model to available tests. Key Words: steel structures, structural connections, end plate connection, beam-to-column connection, moment – normal force interaction, design model, component method.
Steel beam-to-column joints are often subjected to a combination of bending and axial forces. The level of axial forces in the joint may be significant, typical of pitched-roof portal frames, sway frames or frames with incomplete floors. Current specifications for steel joints do not take into account the presence of axial forces (tension and/or compression) in the joints. A single empirical limitation of 10% of the beam's plastic axial capacity is the only enforced provision in Annex J of Eurocode 3. The objective of the present paper is to describe some experimental and numerical work carried out at the University of Coimbra to try to extend the philosophy of the component method to deal with the combined action bending moment and axial force.
This paper presents an experimental study of two full-scale steel beam-column assemblies, each comprising three columns and two beams, to (1) define their response characteristics under a column removal scenario, including the capacity of the beams and their connections to carry loads through catenary action, and (2) provide experimental data for validation of beam-to-column connection models for assessing the robustness of structural systems. The assemblies represent portions of the exterior moment-resisting frames of two ten-story steel frame buildings. One test specimen had welded unreinforced flange, bolted web connections, and the other had reduced beam section connections. When subjected to monotonically increasing vertical displacement of the unsupported center column, both specimens exhibited an initial elastic response dominated by flexure. With increased vertical displacement, the connections yielded, and axial tension developed in the beams. The axial tension in the beams increased until the connections failed under combined bending and axial stresses. The test results show that the rotational capacities of both connections under monotonic column displacement are about twice as large as those based on seismic test data.
A new method, Applied Element Method (AEM) for analysis of structures is introduced. The structure is modeled as an assembly of distinct elements made by dividing the structural elements virtually. These elements are connected by distributed springs in both normal and tangential directions. We introduce a new method by which the total behavior of structures can be accurately simulated with reasonable CPU time. This paper deals with the formulations used for linear elastic structures in small deformation range and for consideration of the effects of Poisson's ratio. Comparing with theoretical results, it is proved that the new method is an efficient tool to follow mechanical behavior of structures in elastic conditions.
A new extension for the Applied Element Method (AEM) is introduced. Using this method, the structure is modeled as an assembly of distinct elements made by dividing the structural elements virtually. These elements are connected by distributed springs in both normal and tangential directions. This paper describes the applicability of the AEM for different fields of analysis and structure types and it deals with the formulations used for RC structures under monotonic loading. It is proved in this paper that the structural failure behavior including crack initiation and propagation can be simulated accurately with reasonable CPU time and without any use of complicated material models.
This two-part paper presents part of the results of a study devoted to the investigation of retrofitting effect of simple steel construction. Through strengthening simple beam-to-column connection, progressive collapse can be prevented by catenary action. The evaluation of catenary action represents a complex analytical problem with a large tension affecting its structural behavior. With the advent of high speed computers and powerful calculation software package, the finite element method offers an ideal tool for tackling such a complex problem. This paper develops sophisticated one-, two- and three-dimensional models of catenary action, and simulates the post-attack behavior of the original and the strengthened structures by means of the ABAQUS finite element package. The global behavior of the one-dimensional beam element model is close to that corresponding to the two-dimensional solid or the three-dimensional shell models, particularly for the structures with strengthened joints. Comparison of results between this study and literature has been carried out for the purpose of validating the present finite element prediction model. Through the comparing computational results before and after strengthening, the advantages of proposed retrofitting scheme are demonstrated.
A generalised component-based model for semi-rigid beam-to-column connections including axial force versus bending moment interaction is presented. The detailed formulation of the proposed analytical model is fully described in this paper, as well as all the analytical expressions used to evaluate the model properties. Detailed examples demonstrate how to use this model to predict moment–rotation curves for any axial force level. Numerical results, validated against experimental data, form the basis of a tri-linear approach to characterise the force–displacement relationship of the joint components. The relationship of the present development to key prior studies of this topic is also explained.
Eurocode 1 -Actions on Structures -Part 1-7: General actions -Accidental actions
EN 1991: Eurocode 1 -Actions on Structures -Part 1-7: General actions -Accidental actions,
EN 1991-1-7, European Committee for Standardization, 2006.
Eurocode 8 -Design of structures for earthquake resistance -Part 1: General rules, seismic actions and rules for buildings, European Committee for Standardization
EN 1998: Eurocode 8 -Design of structures for earthquake resistance -Part 1: General rules,
seismic actions and rules for buildings, European Committee for Standardization, 2004.
Design of end plate joints subject to moment and normal force
- Z Sokol
- F Wald
- V Delabre
- J P Muzeau
- M Svarc
Sokol Z, Wald F, Delabre V, Muzeau JP, Svarc M. Design of end plate joints subject to
moment and normal force. Proceedings of the Third European Conference on Steel Structures
-Eurosteel 2002, Coimbra 2002. Coimbra: Cmm Press; 2002, pp. 1219-28.