Column | EPFL Graph Search

A column or pillar in architecture and structural engineering is a structural element that transmits, through compression, the weight of the structure above to other structural elements below. In other words, a column is a compression member. The term column applies especially to a large round support (the shaft of the column) with a capital and a base or pedestal, which is made of stone, or appearing to be so. A small wooden or metal support is typically called a post. Supports with a rectangular or other non-round section are usually called piers. For the purpose of wind or earthquake engineering, columns may be designed to resist lateral forces. Other compression members are often termed "columns" because of the similar stress conditions. Columns are frequently used to support beams or arches on which the upper parts of walls or ceilings rest. In architecture, "column" refers to such a structural element that also has certain proportional and decorative features. A column might

Déformabilité et capacité portante des colonnes en béton armé

Serge Dal Busco

For buildings which are stabilized by core or shear walls, the vertical members are generally subjected to compressive normal forces N and certain imposed angles of rotation θ. Similar in this respect are non slender bridge piers. These rotations originate from, on one hand, the length variations of the horizontal elements (beams, slabs) due to shrinkage, temperature and prestressing, while on the other hand the bending of these elements due to the vertical loading. Thus, in this case, it is a problem of imposed deformations. However, the usual methods of calculation do not take this fact into account and bring the computation back to a question of forces. In this case, the design is mostly based on the resistance of individual sections, with the use of moment-axial load interaction diagrams MR-NR. In this thesis, a different method is proposed which takes account of the problem of imposed deformations, which concerns equally well the real behaviour of the structure. This proposal is limited to the cases where the slenderness ratio λcr is less than or equal to 50 (λcr ≤ 50). The analysis of a column is carried out considering the vertical load N and the imposed end rotations θ, due to the interaction of horizontal load carrying members. This method allows one to create structures with a greater performance, thanks to the larger distance between expansion joints and to a reduction in the overall dimensions of the columns. This equally has the consequence that the columns are almost always able to be fixed ended by the horizontal members, thus permitting a reduction in their slenderness λcr and which eliminates the costs of the hinge devices. However, it is mostly necessary to resort to high percentages of reinforcement to transmit the elevated vertical loads. This concept of the association of N and 0 is applied to both the examination of the ultimate limit state (loading capacity and deformability) and to serviceability (aptitude of service). The first verification consists of assuring that the column possesses the required deformability to permit the imposed rotations, while transferring the normal force, with the required security. It is possible to obtain this by using adequate transverse reinforcement at the fixed ends of the column, in such a fashion that plastic hinges would be able to form there. The first part of this work concentrates on the development of a method which allows the determination of the characteristics of such a transverse reinforcement (shape and configuration, spacing and diameter of stirrups), as well as an investigation of the numerous parameters influencing the behaviour of columns at the ultimate limit state. In the second part, an explanation is given on how to control the behaviour of a column, when it is subjected to service loading and imposed rotations, in order to verify its serviceability. This explanation takes into account the nature of the rotations, caused by the variations in temperature or by long term phenomena, such as shrinkage and creep. Its application is easy as it is given in the form of charts. Finally, a method for the practical cases is proposed to the designer. It contains the notes and charts to design and verify reinforced concrete columns with different levels of reinforcement.

EPFL1988

Poinçonnement des planchers-dalles avec colonnes superposées fortement sollicitées

Roberto Guidotti

Flat slabs are commonly used in buildings due to their easiness of construction and economy. In order to keep these advantages, columns are usually not continuous through the slabs in multi-storey buildings. In these cases, the slabs are subjected to large compressive stresses at the support area of the columns, which can exceed the uniaxial compressive strength of the concrete of the slab. This critical zone is in addition subjected to large shear forces and bending moments due to the loads applied on the slab. This leads to a series of potential failure modes: crushing of the concrete of the slab between columns, flexural failures or punching shear failures. Most research has previously focused on the influence of bending of the slab on the column strength. However, no works have provided in-depth investigation of the strength of the slab when large column loads are applied. In this research, an extensive experimental program has shown that the stresses applied at the support area of the columns can be significantly larger than the uniaxial compressive strength of concrete. The test results have clearly shown that no special confinement or load transfer devices are required between columns for most cases (moderate column loads). In addition, two phenomena have been observed. The first one is a reduction on the flexural strength as column loads are applied. The second corresponds to a significant increase on the punching shear strength and deformation capacity with column loading. Existing theoretical approaches for flat slab behaviour and strength are shown not to be directly applicable for slabs subjected to large column loading. In this research, the principles of two general theories (the theory of plasticity and the critical shear crack theory) are thus used to investigate such cases. The theory of plasticity allows calculating a plastic failure envelope accounting for bending and column loading, whereas the critical shear crack theory, which in this work as been further investigated theoretically, is used to derive a failure criterion accounting for punching shear failure in presence of column loading. The results for both theories are finally presented in terms of a single interaction diagram between column loading and slab loading (bending and shear of the slab). The theoretical approaches require however the help of rather refined numerical tools for estimating the strength of a flat slab. In order to use the theoretical approaches for design, a simplified approach has been developed, allowing to calculate the strength as well as the deformation capacity of flat slabs. These tools were implemented in a design method for slab-column joints in multi-storey building. This design approach allows to derive simplified interaction diagrams that can be compared with the loading history of the structural element analysed.

EPFL2010

Influence of residual stresses on the buckling capacity of axially loaded steel columns

Gabriele Falconi

Over the past 60-80 years, the design methodology of steel structures comprising conventional steel profiles, such as HEA, HEB or HEM, has remained unchanged. However, during the 21st century, production methods have improved considerably. The aim of this study is to develop the basis for evaluating and refining the design methodology of steel members by considering realistic residual stress distributions generated during the fabrication process. Out of the numerous production methods, in this study we focus on hot rolled wide flange cross sections which are the most commonly used profiles in construction. Design specifications vary from one country to another. A comparison of the Swiss, European, Canadian, and Japanese approaches would help towards understanding the factors influencing the sizing of steel profiles. Simplified methods based on analytical and semi-experimental models have been developed over time to help engineers consider the phenomenon of lateral buckling by ensuring a sufficient degree of safety. Considering that the above design specifications have been developed based on experimental research of steel profiles and materials characteristic of old practices, this study investigates potential updates in the current design practices. To succeed in this challenge, it is imperative that the residual stress distributions of current cross-sectional and material characteristics are explained. Several studies throughout the past years have tried to focus on formulating simplified models that consider residual stress distributions. The accuracy of these models is investigated and recommendations are provided based on the best fits to measured residual stress distributions. These have explicitly been collected from nearly 10 experimental programs leading to more than 30 measured distributions with 𝐻/𝐵 (where 𝐻 is the height of the wide flange section and 𝐵 is the width) ranging from 0.95 to 2.22 (where 𝑡𝑓 is the thickness of the flange) ranging from 6.30 to 40mm. To supplement the knowledge regarding the residual stress distributions of current material specifications and to widen the cross-sectional range of available distributions, five additional wide flange residual stress distribution measurements (i.e., HEA160, HEM500, IPE120, IPE200 and IPE360) are implemented for the sake of this study. These distributions have been precisely determined through destructive laboratory measurements (i.e., cutting method) that are thoroughly explained in this thesis. In the advent of new technology and software development, structural element simulation can be performed in a thorough and precise manner. With the aid continuum finite element analysis (CFEA), the influence of residual stresses on lateral buckling of columns under axial load will be investigated. Eight cross-sectional profiles (i.e., HEA160, HEB500, HEM300, HEM500, IPE120, IPE200, IPE 360 and IPE400) are investigated. The CFEA consider realistic residual stress distributions that have been conducted by RESSLab, EPFL. The ultimate compressive load of these profiles considering varying buckling lengths (𝜆̅𝑘 ranging from 0.49 to 1.93, where 𝜆̅𝑘 is the normalised buckling length) are determined and compared with available design specifications.

2021