Equivalent load of reinforced concrete columns under fire

A joint of lattice aluminium welded structure made of circular hollow sections (CHS) has been analysed. Aluminium alloy EN AW 6082-T6 was used. Calculation of ultimate load bearing capacity of lattice structure web member assumes check of element load bearing capacity for the following calculation situations:- calculation of ultimate load bearing capacity of compressed elements with the influence of buckling,- calculation of ultimate load bearing capacity of compressed elements with the influence of HAZ,- calculation of ultimate load bearing capacity of tensioned elements with the influence of HAZ,- calculation of ultimate element force in truss joint, depending on joint construction.The first three checks are independent of type and characteristics of truss chords. They depend only on elements connection manner and geometrical characteristics of web members. The fourth condition directly depends on relation of chord and web member characteristics, i.e. ratio of their diameters and tube wall thicknesses. The choice of joint geometry, gap between elements in joint as well as joint eccentricity are also important for ultimate force in web member. Check of K-joint ultimate bearing capacity is particularly needed for welded joints due to aluminium strength decrease caused by HAZ (Heat Affected Zone) effect.European standard EN 1999 for aluminium structures design has not defined ultimate load of web members regarding type and characteristics of joint connection.Value of ultimate force in web member of K-joint, depending on connection type, by means of expressions defined in EN 1993-1-8 (Design of steel structures - Part 1-8: Design of joints), has been analysed. Comparative analysis has been done by means of ANSYS modelling, taking into consideration real characteristics of aluminium alloy and ultimate load bearing capacity reduction in the vicinity of weld due to HAZ effect. The main goal of the paper is to analyse capability of expressions from EN 1993-1-8 for steel structures to be used in aluminium structures, having in mind quoted limitations.

The design and assessment of offshore structures, fixed or floating, against extreme and abnormal accidental events require special advanced analysis capabilities and can be dimensioning in certain situations. Such accidental events entail vessel collision/allision, dropped objects, fire, and explosion conditions. Only vessel impact and dropped objects are addressed herein. Allisions involving high impact speeds are also discussed. The structures considered include fixed platforms, floaters (Spar, FPSO, and Semi-submersible), and mobile offshore units. The paper shows how nonlinear FEA and simplified methods are applied both at the design stage and as assessment tools following an incident of accidental loading. It demonstrates that by making reasonable assumptions concerning the energy dissipation parameters during a collision/allision scenario, significant savings in computational and analysis efforts are realized while the reliability of the results is maintained. Both traditional low kinetic energy and abnormal high energy scenarios are evaluated. The paper also presents proposed repair solutions to some typical damage conditions and compares the different codes and standards (ISO, NORSOK, and API) with regards to the acceptability criteria. Introduction The design of offshore structures must account for accidental loadings with low probability of occurrence. Such accidental loadings include vessel collision/allision, dropped objects, fire, and explosion conditions. This paper is dedicated to vessel impact and dropped objects. Fire and blast resistance will be covered in future publications focusing on offshore applications. The FABIG (2009) and ASCE (2010) are currently the two main bodies dealing with fire and blast resistant structures with emphasis on buildings and petrochemical facilities. In addition to accidental supply ship impacts, some recent offshore facilities had to consider high speed ship bow impacts or allusions in order to ensure adequate safety especially when storage of petroleum or liquefied gas is involved. The objective of this paper is to present recent analysis capabilities that make it possible to realistically predict the energy absorption capabilities of offshore structures due to ship collision. This is important in order to ensure that the extent and consequence of the damage is acceptable. The acceptability criteria are set in the regulations and codes of practice as dependent on the associated collision risk level and consequence assessment. In the ISO standards; for example, hazards are categorized into three main groups, according to annual exceedance probability or return period:–Group 1 - hazards with 10–2 annual probability or return period of the order of 100 years–Group 2 - hazards with 10–3 annual probability or return periods of the order of 1000 to 10000 years–Group 3 - hazards with 10–4 annual probability or return periods well in excess of 10000 years Extreme conditions correspond to the 100 year conditions and are treated as ultimate limit state (ULS) events while accidental or abnormal events are associated with the 1000 or 10,000 year abnormal limit state (ALS) scenarios. A review of requirements in offshore regulations, standards and codes is given in Ghoneim (2008).

Modeling elevated-temperature mechanical behavior of high and ultra-high strength steels in structural fire design

Fire resistance of stainless steel beams with rectangular hollow section: Numerical investigation and design

Wind resistant size optimization of geometrically nonlinear lattice structures using a modified optimality criterion method

Topology optimization for concurrent design of layer-wise graded lattice materials and structures

Electric vehicles (EVs) are widely recognized as a key strategy for improving global sustainability; however, their implications for building safety, particularly under fire conditions, require further investigation. This study examines the structural response of reinforced concrete (RC) beams exposed to EV fire scenarios, which are characterized by more severe thermal demands than the ISO 834 standard fire curve adopted in structural fire design, including EN 1992-1-2. A coupled thermal–mechanical finite element analysis (FEA) was performed on nine RC beams, considering variations in reinforcement layout, rebar diameter, and concrete cover thickness. When compared with fire resistance times predicted by standardized design procedures, the numerical results indicate that EV fires accelerate building damage by up to 27% within the first 60 min of exposure. Increasing the concrete cover to at least 30 mm and adopting multiple reinforcement layers were shown to enhance fire performance by reducing heat transfer to the steel reinforcement and lowering stress levels within the cross section. The findings demonstrate that current fire design provisions may underestimate the structural demands imposed by EV fire scenarios. Consequently, this study highlights the need to revise fire resistance criteria and reinforcement detailing rules to ensure adequate safety and resilience of RC structures in sustainable built environments subjected to emerging EV fire hazards.

High strength reinforced concrete (HSRC) has been used more frequently in the construction of high rise buildings and other concrete structures in recent decades due to its advantages and excellent performance over normal strength and conventional reinforced concrete. Some of these advantages include: higher strength, better durability and allowance for provision of using less concrete and smaller section sizes. Although HSRC performs better than normal strength reinforced concrete (NSRC) at ambient temperatures, NSRC has been found to perform better than HSRC at elevated temperatures and fire conditions. Provision of adequate fire resistance for reinforced concrete (RC) structures is essential as fire represents an extreme loading and hazardous condition to which a structure might be exposed during its life span. The fire resistance of RC members is evaluated using a prescriptive approach which is irrational and conservative. Current codes of practice and construction in industry are moving towards performance based fire design method with computing software, which is a rationally based method with each structure designed to meets its own need. This method requires comprehensive knowledge and modelling of concrete and reinforcement material behaviour and their response at elevated temperatures. The fire resistance of HSRC members (columns and beams) in this study was evaluated using a three-dimensional Finite Element (FE) model created in ANSYS. The stress – strain behaviour of concrete proposed in this research was used in modelling the behaviour of concrete in ANSYS, while other concrete and steel material properties were accounted for by using models proposed by other researchers. The fire resistance of the HSRC members is evaluated using coupled field analysis (thermal – structural analysis) with performance based failure criteria provided in the code of practice. The accuracy of the FE model was verified by comparing the thermal response, structural response and predicted fire resistance with fire test results obtained. Using the validated FE model, parametric studies were conducted to investigate the influence of various parameters affecting the fire performance of HSRC members exposed to fire. From the parametric studies conducted, simplified calculation models were developed for evaluating the resistance of HSRC members (columns and beams) exposed to fire. These models were validated with results from ANSYS and a fire resistance test. The simple model accounts for major factors such as member size, load ratio and fire scenario, and therefore can be easily incorporated into structural design. The FE model and simple calculation model provide a rational approach for evaluating the fire resistance of HSRC (members) and predict a more accurate fire resistance than the prescriptive approach.

A set of structural Eurocodes dealing with the basic materials used in construction (concrete, steel, wood, masonry) has been accepted in Europe as a pre-standard. A part of each covers Structural Fire Design. In Eurocode 1, thermal and mechanical actions are given. In Eurocodes 2 to 6, calculation methods for assessing fire resistance of structures can refer either to tabulated data or to simple calculation methods or advanced methods. When fire protection material is needed to increase the fire resistance, necessary data are obtained from fire test results.

In this paper, the shear resistance and design of stainless steel plate girders at elevated temperatures are investigated. A broad range of parameters influencing the structural response of stainless steel plate girders in fire are taken into account, considering (i) austenitic and duplex stainless steel grades, (ii) rigid and non-rigid end posts, (iii) different aspect ratios for the unstiffened portions of the plate girders, (iv) various web slendernesses and (v) different elevated temperature levels. The influence of these parameters on the behaviour of stainless steel plate girders at elevated temperatures is considered. Currently, there is an absence of specific design rules on the fire design of stainless steel plate girders in the European structural steel fire design standard EN 1993-1-2. Considering this, an accuracy assessment of the room temperature stainless steel plate girder design recommendations of the European structural stainless steel design standard EN 1993-1-4 applied with the elevated temperature material properties of stainless steel is performed. The results indicate that this approach leads to unsafe and scattered ultimate strength estimations for stainless steel plate girders in fire. New fire design recommendations for stainless steel plate girders that are in accordance with the existing design provisions of EN 1993-1-2 and EN 1993-1-4 are proposed. The accuracy and safety of the proposed new design recommendations are comprehensively verified against the results from nonlinear finite element modelling.

This paper develops a simplified, but effective, algorithm in obtaining critical slab design moments for parking garages. Maintaining the uniformly distributed load concept generally adopted in the design of building structures, this paper also introduces the equivalent vehicle load factors, which can simulate the vehicle load effects without taking additional sophisticated numerical analyses. After choosing a standard design vehicle of 2.4 tons through the investigation of small to medium vehicles made in Korea, finite element analyses for concentrated wheel loads were conducted by referring to the influence surfaces. Based on the obtained member forces, we determined the equivalent vehicle load factors for slabs, which represent the ratios for forces under vehicle loads to these under uniformly distributed loads. In addition, the relationships between the equivalent vehicle load factors and sectional dimensions were also established by regression, and then used to obtain the proper design moments by vehicle loads. The member forces calculated by the proposed method are compared with the results of four different approaches mentioned in current design codes, with the objective to establish the relative efficiencies of the proposed method.

In coastal areas, large-span space steel net trusses experience structural deformation due to strong winds. Currently, the application of equivalent static wind load to the structure does not consider the influence of local forces. The local uneven force on the bars caused by the structural appearance is ignored, complicating the identification of local deformation in the net truss. Additionally, this simplification increases the difficulty in evaluating wind load-sensitive areas of the building. This paper introduces a novel method for calculating static equivalent wind load, considering the transmission relationship between the structural roofs appearance and the internal truss forces. Following the outlined methodology, wind load is precisely applied at nodes with diverse windward faces, taking into account the node area ratio. The paper also examines how varying standard wind load values affect mesh truss deformation under different wind angles. Results indicate that, at 0o, 90o, 180o, and 270o wind directions, wind load-sensitive areas are linked to roof shape and structural characteristics. Maximum displacement in the truss grid’s overall structure primarily occurs in the windward corner contact area. Network truss deformation linearly increases with the load standard. If the wind load exceeds 1.0 kN/m2, deformation is associated with the windward vertical plane’s area and steel column spacing, impacting overall structural safety.

Using several formulas of across-wind aerodynamic forces and aerodynamic damping of rectangular super-high-rise buildings with side ratios smaller than 2 proposed previously by the authors, across-wind equivalent static loads and responses of super-high-rise buildings are evaluated through a proper combination of resonant and background components. The resonant component is computed according to the power spectral density of the base moment and the aerodynamic damping. The background component, whose vertical distribution is derived from background moment responses at different heights and then expressed as a cubic equation of the relative height, is computed using the base moment coefficients. Furthermore, comparisons are made for the equivalent static wind loads and responses of a hypothetical typical building between the present method and the AIJ (1996) method, which indicate the applicability of the present method. Finally, the effects of background component and aerodynamic damping on the equivalent wind loads and responses are also discussed.

Three-center cylindrical latticed shell closed cargo shed is a typical wind-sensitive structure, and wind load is one of the control loads in structural design. Based on the background of three three-center cylindrical latticed shell closed cargo sheds in a comprehensive wharf project, wind tunnel tests and numerical analysis on various factors affecting wind load of closed sheds were carried out. The influence of the ventilation roof, the opening and closing of doors and windows, the interference between three sheds, and the wind speed reduction related to wind directions on the wind load of the closed cargo shed was studied, the calculation results of closed cargo sheds designed by the wind load in wind tunnel test results, load codes and related literature are compared. Through the research, it is found that the ventilation roof, the opening and closing of doors and windows, the interference between three sheds, and the wind speed reduction related to wind directions had great influence on the wind tunnel test results, there were potential safety hazards in the structural design of closed sheds by the wind load in load codes and related literatures, the wind tunnel test of this kind of long-span closed sheds should be conducted before the detailed design, and the various actual working conditions of the sheds should be taken into account and correctly reflected during the wind tunnel test.

Gust response envelope approach to the equivalent static wind load for large-span grandstand roofs