China
Africa
Explore chapters and articles related to this topic
Instability of struts and frameworks
Published in R.C. Coates, M.G. Coutie, F.K. Kong, Structural Analysis, 2018
R.C. Coates, M.G. Coutie, F.K. Kong
If the member is perfectly straight, axial load P acting on its own would produce no lateral deflections. Lateral loads WI and W2 acting on their own would produce lateral deflections, and these would be increased if the member were to carry both axial compressive and lateral loads at the same time, or decreased for an axial tensile load. The deflections of the one loading case cannot therefore be superimposed on those of the other. Even without the presence of forces W, lateral deflections would be caused by P if it were eccentric to the column centroid (the column then would carry an axial load, plus an end moment) or if the column had an initial curvature. In all these cases the lateral deflections would be related to the value of the axial load in a nonlinear manner, even if the material of the column were linearly elastic, as was shown in Section 4.5. Columns are very common in structural engineering, and an understanding of their behaviour is vital to the designer. He may try to load columns centrally, but fabrication tolerances prevent this from being achieved exactly and no column is perfectly straight. In general, he recognizes that columns are imperfect, and may be required to carry moments, and designs accordingly. The real problem is therefore the study of imperfect, eccentrically loaded columns, but to gain a full understanding it is instructive to look first at the behaviour of columns which are ideal. It will be assumed in the following analysis that: (a) The ends of the strut are mounted in perfectly smooth pinned supports.
Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
A column is an initially straight load-carrying member that is subjected to a compressive axial load. The failure of a column in compression is different from one loaded in tension. Under compression, a column can deform laterally or buckle, and this deflection can become excessive. The buckling of columns is a major cause of failure. To illustrate the fundamental aspects of the buckling of long, straight, prismatic bars, consider a thin meter stick. If a tensile axial load is applied to the meter stick, the stable equilibrium position is that of a straight line. If the stick is given a momentary side load to cause a lateral deflection, upon its release the stick immediately returns to the straight line configuration. If a compressive axial load is applied, a different result may occur. At small axial loads, the meter stick will again return to a straight line configuration after being displaced laterally. At larger loads the meter stick will remain in the displaced position. With an attempt to increase the axial load acting on the buckled column, the lateral deformations become excessive and failure occurs.
Ductility Enhancement of Concrete Members under Blast Load Using CFRP External Strengthening
Published in Jaap Bakker, Dan M. Frangopol, Klaas van Breugel, Life-Cycle of Engineering Systems, 2017
Husham Alamnsour, Zoubir Lounis, Bessam Kadhom
Columns are the most critical elements in structural systems of many facilities such as buildings and bridges. They may fail catastrophically in buildings exposed to bomb blast, which could lead to the progressive collapse of the entire structure. Past global blast events have shown that preventing progressive collapse would significantly reduce the number of casualties and minimize the structural damage. Hence, columns in existing critical facilities must be upgraded to ensure they provide adequate robustness under the effects of blast loads in order to minimize the fatalities, injuries and damage costs. To predict the dynamic behavior of reinforced concrete (RC) structures under blast, a single-degree-of-freedom (SDOF) model has been widely used. However, in a SDOF analysis, the force-displacement relationship (also called resistance function) of the structural member must be identified. An idealized resistance function can be established by simply specifying the moment capacity and the corresponding curvature for the section at different load levels, such as yield level (My) and ultimate level (Mu) (ASCE 2011 as well as the equivalent plastic hinge length (Lp). This length can be predicted using one of the models available in the literature.
Optimisation of life-of-mine production scheduling for block-caving mines under mineral resource and material mixing uncertainty
Published in International Journal of Mining, Reclamation and Environment, 2022
Roberto Noriega, Yashar Pourrahimian, Eugene Ben-Awuah
Production scheduling is carried out over a 10 year horizon, in this particular case selected to be able to experiment extensively, however could be extended for longer periods to cover the life-of-mine. The production unit dimensions for aggregating resource blocks into columns are set at 20 m by 30 m to represent column extraction units in caving mines. The maximum column height is set at 300 m with a minimum column height of 60 m. These guarantee that if the optimisation model decides to open up a production unit at the undercut level, it will draw material from it until at least a height of 60 m and up to 300 m with the capability of stopping anywhere in between. The maximum adjacent relative height of draw, which represents the difference in the height of draw between a given PU and its adjacent ones, is set to 60 m. The selected PU dimensions provide a cave back slope of between 60° to 70°. The minimum draw rate per column is set to 70 kton/period, which is equivalent to a draw height of 30 m, with a maximum draw rate of 140 kton/period equivalent to a 60 m draw height. These parameters would be adjusted to reflect a given project’s geotechnical environment to guarantee good flow conditions for the broken ore. Based on these dimensions, the case study comprises 108 PU, representing drawpoints, and 864 MU representing slices to be extracted. The maximum undercutting rate is set at 9600 m2/period, which restricts the amount of PU and undercut area that can be developed in any given period.
Damages and Failures of Structures in İzmir (Turkey) during the October 30, 2020 Aegean Sea Earthquake
Published in Journal of Earthquake Engineering, 2023
Tuba Gurbuz, Abdullah Cengiz, Sener Kolemenoglu, Cem Demir, Alper Ilki
Columns are the vital vertical structural elements, whose failure may cause severe damage or collapse of the whole structure. In the current design approach for moment resisting frame structural systems, the aim is to have formation of the plastic hinges at beam end regions rather than columns and joints. This can be achieved by establishing a strength hierarchy among beams and columns joining at a beam-column joint. In other words, columns should be stronger than beams. In Turkey, the capacity design principles were introduced to reinforced concrete design by the issuing of TSDC1998 (1998). During the site visits, it was observed that seismic damages were mostly concentrated at columns rather than beams. Some severe column failures are presented in Fig. 27.
Axial Behaviour of Glass Fibre Reinforced Polymer-Confined Reinforced Concrete Short Columns
Published in Structural Engineering International, 2018
Mini Soman, Chandrasekharannair Rajalekshmiamma Chandrakumar
Concrete is the most versatile building material of the recent past. But due to aggressive environment, pollution, earthquake, overloading and misuse, the concrete structures start showing distresses in the form of cracks, delamination and collapse. Columns are one of the most critical structural members with high importance in a structure, and their failure can cause partial or total collapse of the whole structure. Hence, the development of a reliable and cost-effective method to repair and strengthen the existing columns is a necessity.