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Unbraced one-bay composite frames are an interesting load-bearing structure for buildings with up to three storeys. However, their fire design is demanding given the lack of simplified design methods. This paper aims to deepen the understanding of the load-bearing behaviour of both unbraced and braced frames when exposed to fire.

In a previous paper, a numerical model for the fire design of these frames was established and validated with good agreement against fire tests. In the current paper, this model was used to compare the typical differences between braced, semi-braced and unbraced composite frames under fire conditions. Further studies addressed the effect of different heating regimes, i.e. partial fire exposure of the columns in the frames and varying location of the ISO standard fire.

Numerical investigations showed that it is necessary to take local failure and deformation limits of the fire-exposed frames into account. On this basis, unbraced composite frames can compete with braced frames as they have to endure less thermal restraints than braced frames.

In contrast to other investigations on frames, the numerical model is able to take into account the shear failure, which is especially important within the frame corners. Using this model, it is shown that limited sway is reasonable to reduce thermal restraints and hence local stresses. In this regard, the concept of semi-rigid composite joints with a distinct amount of reinforcement has proven to be very rational in fire design.

The collapse of a structure resulting from the instability of steel frames due to fire is the worst failure mode to consider in fire-structural engineering, and should be avoided. The purpose of this paper is to propose a new method for estimating the minimum possible duration of a fire event that could result in the instability of an unbraced steel frame.

The proposed method is in the form of a constrained minimization problem that determines the worst case fire scenario that can cause instability of a structure, and is solved using nonlinear constrained mathematical programming algorithms. The formulation is demonstrated via a numerical example.

For frames subjected to fire events modelled with monotonically increasing fire curves, the worst case fire causing instability of a frame is always one where all of the compartments catch fire at the same time. For frames subjected to fire events where fire curves decay, the minimization problem must be solved rigorously. The results are significantly affected by the fire curves and amount of insulation applied to each member.

The proposed method is an extension of a method previously established by Xu et al. (2018) to assess the stability of unbraced steel frames subjected to elevated member temperatures. The previous method does not consider fire duration and heat transfer mechanics, which are included in the proposed method. The proposed method is potentially useful for designers in conducting fire scenario analysis in the performance-based design of structures.

The purpose of this study is to gain a deeper understanding of the structural behaviour of fire-exposed unbraced composite frames. Designers to date paid little attention to unbraced one-bay composite frames as structural system. There are two main reasons for this. First, codes lack simplified methods for the fire design of these frames due to their sway and the linked P-Δ effects when subjected to fire, which complicates the design. Second, it is demanding to construct external composite joints for the regarded one-bay frames. Thus, external joints in composite constructions are mostly constructed as steel joints. Nevertheless, these frames offer advantages. These include increased usable space and flexibility in the building’s use, large spans, fast construction times and inherent fire resistance.

To profit from these benefits, two different external semi-rigid composite joint were developed for the considered one-bay composite frames. The first solution based on concrete-filled steel tube columns and the second on concrete-filled double skin tube columns. Furthermore, a numerical model was established to study the fire performance of unbraced composite frames. The model was validated against four fire tests on isolated composite joints and two large-scale fire tests on unbraced composite frames.

Overall, the predictions of the numerical model were in good agreement with the test results. Thus, the numerical model is appropriate for further investigations on the fire performance of unbraced composite frames.

The sequence of construction results in significant stresses in the steel section, which creates difficulties in numerical modelling and may account for the relatively few studies carried out at room temperature. For the fire design, there was, to the best knowledge of the author, to date no numerical model available that was capable of considering the sequence of construction.

The author is Professor of Aeronautical Engineering and Applied Mechanics at the Brooklyn Polytechnic. He is well known to the British aero‐nautical world not only for his writings but as a fluent and stimulating speaker. In this volume Professor Hoff develops a system of analysis starting from the principle of virtual displacements. In the first of the four Parts this principle is explained and, after a brief glance at its application to mechanisms, is used to find the forces and displacements in jointed frameworks. The principle is applicable to both simply stiff and redundant frames. An engine mounting under torque loads from a radial engine is discussed in full detail to illustrate the application to a redundant space frame with the aid of tension coefficients. This Part ends with the treatment of beams by virtual displacements, the Hardy Cross moment distribution method and the analysis of the rigid unbraced frame.

THERE are two outstanding principles which underlie all airship design, two criteria by which everything undertaken may bo judged. The first is that the body produced shall offer a minimum of resistance to propulsion through the air; the second is that, having shaped a body in that way, it shall give a maximum of disposable lift for a given volume. An airship also, at the present time at least, must be produced for a minimum of cost. For this reason every effort must be made to design the structure as cheaply, as economically, and as quickly as possible.

Introduction The 1985 earthquake in Mexico City served as a sobering reminder of the destructive effects that earthquakes can have on well‐constructed and engineered buildings. The collapse of some 120 tall buildings in steel and reinforced concrete, many designed to a modern earthquake building code, and serious damage in several hundred more, might suggest that modern methods are powerless to prevent catastrophe in an extreme event. Less informed observers even concluded (erroneously) from the generally good performance of 18th and 19th century masonry buildings in the earthquake that we have somehow lost the art of earthquake resistant design which our fore‐fathers knew. The reasons for the selectiveness of attack and the poor performance of modern construction in the Mexico earthquake have been widely discussed (for example, Booth et al.1) and are reasonably well understood.

Introduction In a previous paper, I discussed the techniques for ensuring the earthquake resistance of new buildings. Experience of past earthquakes demonstrates that incorporating the methods and advances of the last 30 years in the planning, design and construction of new buildings is the best way of minimising loss of life and investment during major earthquakes.

The purpose of this paper is to detect damages in steel structures with actual connections, i.e. semi-rigid connections. The method will detect the damages by tracking the changes in the stiffness of structural members using only a limited number of dynamic responses and without knowing the type or time history of the dynamic force applied on the structure.

The paper proposes a technique that combines the iterative least-square and unscented Kalman filter (UKF) methods to identify the stiffness of beams and columns in typical two-dimensional steel-framed structures with semi-rigid connections. The detection of damages is by using nonlinear time-domain structural health monitoring method.

The technique is verified by using numerical examples using noise-free and noise-included dynamic responses from two different types of dynamic forces: harmonic and blast loads. The results showed that the UKF method with iterative least-square is a powerful approach to identify and detect damages in structures that have nonlinear behavior and the method was able to detect the damages in beams with a very high accuracy for noise-free and noise-included dynamic responses. In addition, the optimum number and locations of dynamic responses (accelerometer sensors) required for damage detection were determined.

This paper fulfills an identified need to detect damages in steel structures using only a limited number of accelerometer sensors.

This publication is a record of a systematic study by records of pressure as a function of time of the cooling effect of the walls of a closed metal vessel in which the explosion of a mixture of air and hydrocarbons is obtained by an electric spark.

Genetic Algorithm, as a generalized constructive search method, has already been applied to various fields of optimization problems using different encoding schemes. In conventional GAs, the optimum solution is usually announced as the fittest feasible individual achieved in a limited number of generations. In this paper, such a pseudo‐optimum is extended to a neighborhood structure, known as optimal design family.

In this paper, the constructive feature of genetic search is combined with trail update strategy of ant colony approach in a discrete manner, in order to sample more competitive individuals from various subspaces of the search space as a dynamic‐memory of updating design family.

The proposed method is applied to structural layout and size optimization utilizing an efficient integer index encoding and its appropriate genetic operators. Different applications of the proposed method are illustrated using three truss and frame examples. In the first example, topological classes are identified during layout optimization. In the second example, an objective function containing the stress response, displacement response, and the weight of the structure is considered to solve the optimal design of non‐braced frames. This approach allows the selection of less sensitive designs among the family of solutions. The third example is selected for eigenvalue maximization with minimal number of bracings and structural weight for braced frames.

In this paper, a pseudo‐optimum is extended to a neighborhood structure, known as optimal design family.