Ove Lagerqvist

Resistance of I-girders to concentrated loads

This paper presents the results from an experimental investigation including tests with welded girders and rolled beams subjected to three different cases of concentrated loads applied to the girder flanges. The welded girders were made from a high strength, quenched and tempered steel, while the rolled beams were of an ordinary steel grade. The results from the experimental investigation presented herein have been added to test results taken from the literature and used for a formulation of a design procedure for the resistance to concentrated loads. The suggested design procedure is unified for the three different load applications and also harmonized with the design procedures normally used for describing buckling problems in the steel codes. The design procedure is a further development of the design procedure for patch loading suggested in B. Johansson & O. Lagerqvist [J. Construct. Steel Res., 32 (1995) 69–105] and has in a simplfied form been suggested for use in Eurocode 3 Part 2 (Bridges), as well as in Eurocode 9.

Resistance of plate edges to concentrated forces

Abstract The prediction of the resistance of plate edges to concentrated loads has been dealt with in numerous studies of a more or less empirical nature. The normal approach is to use two criteria for the resistance, one based on yielding and one based on instability. This study aims at a procedure that is harmonized with those normally used for describing other buckling problems. It has been carried out as part of the work with drafting Eurocode 3 Part 2 and the paper is intended as a background document for the suggested design rules.

Critical buckling of longitudinally stiffened webs subjected to compressive edge loads

The resistance of steel plate girders subjected to concentrated load can be described using a strength curve, which includes a gradual transition from yielding to buckling depending on the slenderness ratio of the web. The slenderness is a function of the ratio of the yield resistance to the critical buckling load. This paper describes a methodology for the determination of buckling coefficients for longitudinally stiffened plate girders subjected to partial edge loading or concentrated loads. After an extensive parametric analysis, the optimum parameters that govern the change from a global buckling mode to a more local buckling mode were found. As in similar buckling problems, the results show that the location and the relative flexural/torsional rigidity of the stiffener are relevant parameters that govern the final buckling shape. Finally an expression for the buckling coefficient used to determine the critical buckling load for longitudinally stiffened girder webs is presented.

Behaviour of girder webs subjected to patch loading

Abstract This paper concerns the behaviour of bridge girder webs subjected to concentrated forces that are introduced in the web during launching, a load case usually referred to as patch loading. So far, this type of loading has, in engineering practice, been dealt with using formulas originating from investigations concerning the ultimate load carrying capacity. Numerous bridge launchings have, however, led to unwanted damages of the girder web, i.e. plastic deformations of such magnitudes that the webs had to be repaired. To avoid these damages it is necessary to have a design method, for launching situations, which focuses more on avoiding some irreversible behaviour than on the ultimate load carrying capacity. Such a design method has to be based on a deeper understanding of the behaviour of the girder. In Ref. [1] the first author discusses the fact that yielding of the flange occurs only after the web plate has been severely damaged. This paper describes the deformation behaviour of the web plate due to patch loading. For small loads the deformations will be similar to the first linear buckling mode. As the load increases a smaller buckle, in the opposite direction, will start to develop in the web plate close to the load. This behaviour, which may be named post-critical buckling, occurs also for girders of a perfectly elastic material. The investigations are based on laboratory tests and non-linear finite element analyses of three typical girders representing different slenderness categories.

Experimental investigation of the behavior of extra high strength steel

This paper comprises a study concerning the mechanical behavior of extra high strength steel. This is investigated by means of biaxial testing of flat cross-shaped specimens in the full σ1-σ2 plane, a concept developed earlier at Steel Structures, Luleå University of Technology. Furthermore, new specimen designs had to be developed to enable testing of a material with high yield strength and low ultimate over yield strength ratio, such as the extra high strength steel Weldox 1100. The tests are performed in two steps: one initial loading followed by unloading and a subsequent loading in a new direction. The test results, containing data from 15 biaxial tests, are characterized by a slightly anisotropic initial yield criterion where the proof stress in compression is consequently somewhat higher compared to the results in tension. In the subsequent loading the observed phenomena are a Bauschinger effect in the direction opposite the initial loading direction and that the transition from elastic to plastic state in subsequent loadings is gradual and direction-dependent.

Using visualization technologies for design and planning of a healthy construction workplace

Purpose – The purpose of the paper is to investigate how health and safety gains and improvements of the construction workplace can be made through the use of three‐dimensional (3D) and four‐dimensional (4D) visualization technologies.Design/methodology/approach – The methodology used in the paper was a combination of semi‐structured interviews with five construction project planners from three construction projects and observations of a 4D model used in one of the three projects.Findings – The findings of the paper have shown a great potential for 3D and 4D visualization in terms of communicating construction information as well as the health and safety risks in the design process where clash detection, work tasks sequence, workspace congestion can be identified by project stakeholders who are thus able to plan for alternative solutions to reduce or eliminate rework, heavy material handling and repetitive and awkward postures which expose workers to musculoskeletal injury risk.Research limitations/implic...

A Probabilistic Approach for Evaluation of Radon Concentration in the Indoor Environment

An analytical method based on structural reliability has been developed with the objective to ensure a healthy indoor environment for people in residential buildings. The method has been applied to a model of the foundation of a house, which is principally a concrete slab on the ground, when the hazard to the indoor environment is radon. The reasons why radon is found indoors have been identified using fault tree analysis. Random variables in the model are defined such that resistance is the ability of people to withstand the radon concentration indoors without adverse health effects and the load effect is equal to the top event of the fault tree and is a function of the environmental load and the decisions made in the building process. A quantitative evaluation was made using both Monte Carlo simulation and First-order second-moment theory where the load effect is compared with the resistance defined as the threshold value for radon concentration indoors stated in the Swedish Building Regulations. The objective was to calculate the probability for exceeding the threshold value and to estimate analytically the safety index. Other interesting areas of application of the developed model could be for the environmental impact from moisture causing growth of micro-organisms and release of chemical emissions, or from soil contaminates like, for example, petroleum products.

Resistance of bridge girder webs subjected to concentrated forces

A model for the ultimate resistance of bridge girder webs to concentrated forces that are introduced in the web during launching is presented. The model is formulated on the basis of observations f ...