Robust design of steel and concrete composite structures

Accidental events, such as impact loading, are rare events with a very low probability of occurrence but their effects often leads to very high human losses and economical consequences. An adequate design should not only reduce the risk for the life of the occupancy, but should also minimize the disastrous results and enable a quick rebuilding and reuse. A robust design prevents the complete collapse of the structure when only a limited part is damaged or destroyed. Design against disproportionate collapse is usually based on the residual strength or the alternate load path methods. Identification of an alternate path may lead to an effective and cost efficient design for progressive collapse mitigation by redistributing the loads within the structure. The continuity of the frame and of the floor represent essential factors contributing to a robust structural response. They in fact enable development of 3D membrane action. A European project focusing on robustness of steel and steel and concrete composite structures subjected to accidental loads is still ongoing. In the framework of the project the authors concentrated their studies on the redundancy of the structure through slab-beam floor systems as well as through ductile joint design. At this aim, two 3D full scale substructures were extracted from a reference building and experimentally investigated with the purpose to get an insight into the mechanisms allowing the activation of the alternate load paths resources, when a column collapse. The paper illustrates the main features of both the specimens tested and the experimental campaign. The preliminary results of the tests are presented and discussed

Numerical models for the analysis of shear walls in light steel residential buildings

AbstractIn recent years, the use of steel light housing structural solutions made of cold‐formed thin‐walled profiles (CFS) is becoming increasingly popular. Lightness, high structural efficiency, durability, rapidity and simplicity of erection of the building and its finishes are some of the main advantages of these systems, which make them attractive and competitive with respect to more traditional constructional solutions. In these buildings, which do have a skeleton made of cold‐formed steel profiles completed by sheathings made of various materials, the key role of transmission of both vertical and horizontal loads from the floors to the foundation, is played by the shear walls. Recently, the University of Trento carried out a project aimed to develop an industrialized housing system made of CFS members. In this framework, experimental and numerical studies of the in‐plane lateral response of shear walls were performed. In particular, this paper summarizes first the experimental program and then it focuses on the main features of numerical models and on their validation in both monotonic and cyclic regime. The critical parameters governing the response of these complex systems are finally identified and discussed

Experimental assessment of an asymmetric steel–concrete frame under a column loss scenario

Several noteworthy accidents clearly pointed out the risk of disproportioned collapse of framed structures. Design codes recently recognized it by adding a new requirement: the structural robustness. Among the different approaches to check robustness, the most popular is associated with the column loss scenario: the analysis should verify that, in case of a column loss, an alternative load path does exist, limiting the portion of structure affected by collapse. Consequently, numerous experimental and numerical studies of 2D and 3D structures were carried out in recent years to identify the mechanism of load transfer from the damaged to the undamaged part of the structure. This knowledge becomes an essential and fundamental key for assuring adequate resistance against progressive collapse by the development of catenary action in the beams and membrane action in the floor slab. Studies of reinforced concrete systems and of bare steel sub-assemblies are numerous. More recent is the focus on the response of steel–concrete composite structures subjected to accidental events. Furthermore, most of these studies focused on the characterization of 2D sub-assemblies or 3D in-scale framed structures. This paper presents an experimental assessment of the structural response of a 3D full-scale steel and concrete composite frame under the column loss scenario. The results are finally compared with the response of a frame with the same overall geometry but different columns’ layout, tested by the Authors within the same research programme

Perforated TWCF steel beam-columns: European design alternatives

Steel storage racks are lightweight structures, made of thin-walled cold-formed members, whose behaviour is remarkably influenced by local, distortional and overall buckling phenomena, frequently mutually combined. In addition, the need of an easy and rapid erection and reconfiguration of the skeleton frame usually entails the presence of regular perforations along the length of the vertical elements (uprights). Holes and slots strongly influence their behaviour, whose prediction is however of paramount importance to guarantee an efficient design and a safe use of racks. This paper focuses on the behaviour of isolated uprights subjected to both axial load and bending moments, differing for the cross-section geometry and for the regular perforation systems. According to the European standards for routine design, four alternatives to evaluate the bending moment–axial load resisting domains are shortly discussed and critically compared in terms of member load carrying capacity

An experimental investigation on solid and perforated steel storage racks uprights

Thin-walled cold-formed (TWCF) profiles are extensively used in adjustable selective pallet racks that represent the most common typology between the logistic solutions. In these structures, vertical members (uprights) are usually channels, often provided with intermediate stiffeners, rear flanges and additional lips. Furthermore, in order to allow for a rapid connection with beams and bracing components, usually uprights present regular perforation systems along their length. Nowadays, theoretical approaches available to design TWCF members are based on equations valid only for few unperforated (solid) cross-section geometries. As a consequence, rack manufacturing engineers frequently adopt the well-known design-assisted-by-testing approach to overcome this limitation and to assess accurately member performance. This approach, time consuming and cost demanding, stresses the need of further improvements required to cover aspects currently not considered in design codes. The paper summarizes the results of a study focused on the response of a commercial upright profile. In particular, 48 compression and 24 bending tests on perforated and unperforated profiles have been carried out. A summary of the experimental program is proposed together with the re-elaboration of test data. Furthermore, the influence of perforation is discussed as well as key design geometric parameters. Finally, owing to the lack of information in major rack standard codes, three different proposals to evaluate the effective second moments of area have been developed, discussed and applied, hoping to contribute to standard improvements

Isoparametric Spline Finite Strip Method for In-plane Stress Analysis (No. R848)

The finite strip method has proved to be an accurate and efficient tool for the analysis of structures having regular cross-section and mechanical proprieties along the longitudinal axis. The spline finite strip method has furthermore proved to be a more flexible tool for the analysis of structures with general support conditions and, utilising the isoparametric mapping, structures with a geometry varying along the longitudinal direction, such as curved slab bridges. In this report, the isoparametric spline finite strip method is applied to the analysis of plate containing cut-outs of different shape and subjected to in-plane stresses. The mapping technique and the theory for the general in-plane stress condition are outlined, as is a novel method for assembling the strips in order to model the particular case of a cut-out. To prove the reliability of the isoparametric spline finite strip method, three different shapes perforation in rectangular plates in traction are analysed. The shapes of the cut-outs presented are a circular, a rectangular and a key shaped hole. The result are compared with exact solutions and finite element analyses

Robust impact design of steel and composite building structures: the alternate load path approach

peer reviewedVulnerability of structures to progressive collapse and mitigation of the effects of local damages are topics widely discussed. The studies worldwide carried out allowed identifying different design strategies. However, specific knowledge is still limited and this gap is apparent in codes of practice. A European project focusing on robustness of steel and steel and concrete composite structures regarding the effects of impact recently started combining the 2 methods of residual strength and alternate load path. In the framework of the project activities, the Authors aimed their studies on the redundancy of the structure through slab-beam-systems and ductile joint as well as on the local behaviour of the impacted members. For this analytical, numerical and experimental investigations have been planned and executed. The paper describes the experimental activities related to the investigations on the structural redundancy and presents the preliminary test outcomes

The FAILNOMORE project - Practice-oriented design recommendations against progressive collapse in steel and steel-concrete buildings

peer reviewedStructural robustness is a specific safety consideration which is currently addressed in modern codes and standards, including the Eurocodes. It requires particular care from all professionals involved in the construction industry. The need for practical guidelines to mitigate the risk of progressive collapse has been emphasised by re cent catastrophic events such as the 9/11 terrorist attack in New-York. The lack of consistent design rules for practitioners is however clearly identified in existing nor mative documents and literature. Accordingly, various research projects were launched, particularly in Europe through RFCS research projects. Thanks to these research activities, significant scientific background has been developed, with the aim of understanding and characterising the behaviour of steel and composite struc tures subjected to exceptional events such as impact, explosion, or loss of a bearing member. Nevertheless, there was a need to consolidate the available scientific knowledge and to transform it into a consistent set of practical recommendations in order to facilitate the design of steel and composite structures for robustness. This was the purpose of a recent RFCS project “FAILNOMORE” (grant No 899371) which was concluded in June 2022. A brief summary and discussion of the main outcomes of this project are provided in the present pape