D. Oehlers

Elementary Behaviour of Composite Steel and Concrete Structural Members

Preface Notation Introduction Sizing of Members Elastic Analysis of Composite Beams Rigid Plastic Analysis of Simply Supported Beams Mechanical Shear Connectors Transfer of Longitudinal Shear Forces Stocky Columns Slender Columns Post-Cracking Dowel Strength Rigid Plastic Analysis of Continuous Composite Beams Lateral-Distortional Buckling General Fatigue Analysis Procedures Fatigue Analysis of Stud Shear Connectors Index.

Elastic buckling of unilaterally constrained rectangular plates in pure shear

Abstract For a certain class of systems, the buckling response may be unilateral rather than bilateral. Unilateral buckling is a contact problem whereby buckling is confined to take place in only one direction. For plate structures, this can occur when a thin steel plate is juxtaposed with a rigid concrete medium, and the steel may only buckle locally away from the concrete core. Examples of this include composite profiled beams, walls and concrete-filled steel tubes, as well as reinforced concrete beams that are strengthened and stiffened by gluing and/or bolting steel plates to their sides. This paper presents a Rayleigh–Ritz method of the local buckling analysis of rectangular unilaterally restrained plates in pure shear. The displacement functions are modelled as polynomials, and the restraining medium as a tensionless foundation. The method presented is shown to be very efficient computationally, and elastic local buckling coefficients are presented for a variety of restraint cases for various plate aspect ratios. The use of these coefficients in determining limiting width to thickness ratios is demonstrated.

Development of design rules for retrofitting by adhesive bonding or bolting either FRP or steel plates to RC beams or slabs in bridges and buildings

Bonding plates to reinforced concrete (RC) structures is a mechanically efficient form of retrofitting that is also inexpensive and unobtrusive. However, bonding plates to RC structures is an extremely complex engineering problem as research has shown that bonded plates are prone to about 30 mechanisms of failure. This paper describes the various techniques of plating that are now available for retrofitting, illustrates some of the various failure mechanisms that can occur and the development of their design rules, and discusses the choices between adhesive bonding and bolting, and the choice between steel and fibre reinforced plastic (FRP) plating.

The Tension Stiffening Mechanism in Reinforced Concrete Prisms

Tension stiffening is an important phenomenon in reinforced concrete because it controls not only deflections but also crack spacings, crack widths and the formation of multiple cracks. It is now common practice to study the effects of tension stiffening in concentrically loaded prisms, which is the subject of this paper, and use these behaviours as guidance for the effects of tension stiffening in reinforced concrete beams. As tension stiffening is a mechanism for stress transfer between the concrete and reinforcement, the interface bond stress-slip (τ–δ) properties are of utmost importance. In this paper, partial interaction theory is used to develop generic closed form solutions for crack spacings and widths, the load to cause primary, secondary cracks and subsequent cracks. Four different types of interface bond characteristics (τ–δ) are considered: a linear ascending bond slip which is useful at serviceability; a linear descending bond slip which is useful at the ultimate limit state; a nonlinear bond slip characteristic which closely resembles material bond slip behavior at all limits; and the CEB-FIP Model Code 90 (CEB 1992).

A structural engineering approach to adhesive bonding longitudinal plates to RC beams and slabs

Retrofitting by plating structures has been found to be very efficient. However, tests have shown that externally bonded longitudinal plates are prone to premature debonding. Furthermore, a comprehensive study of published research has also shown that there can be large discrepancies between debonding mathematical models and tests. To overcome this problem and to allow structural engineers to adhesively bond plates with safety and efficiently, a structural engineering approach is suggested whereby many of the debonding mechanisms can be prevented by judicious detailing; this approach can be applied to tension face plates, compression face plates, side plates, U-sectioned plates, and angle-sectioned plates. Four continuous reinforced concrete beams have been retrofitted with adhesively bonded longitudinal plates and tested in order to illustrate this design approach, to directly compare the performance of longitudinal side plates with longitudinal tension face plates, to compare FRP plating with steel plating, and in particular to illustrate the effect of debonding on the sectional ductility of longitudinally plated continuous RC beams.

PARTIAL-INTERACTION ANALYSIS OF COMPOSITE BEAM/COLUMN MEMBERS*

ABSTRACT Members in which two or more elements are bolted together to form composite structures that are stronger, stiffer, and more ductile than the sum of the individual elements are now commonly used in practice, not only for new structures but also, more recently, for the retrofitting of existing structures. The shear connectors that are used to tie the elements together rely on slip, that is partial interaction, to transfer the longitudinal shear. This makes the behavior of composite structures complex, so that most composite structures are designed assuming no slip, full interaction, which gives an upper bound to the strength and stiffness. In order to determine the true strength, to estimate the amount of slip to prevent fracture of shear connectors due to excessive slip, and to ensure that plated reinforced concrete columns can achieve their required seismic ductility, it is necessary to allow for slip in the mathematical model. In this paper, the classic linear-elastic partial-interaction theory for composite steel and concrete beams is extended to allow for axial forces, as occur in plated reinforced concrete columns and prestressed composite beams, and also to allow for boundary conditions associated with plastic hinges. Furthermore, a set of generic parameters that govern the fundamental response of the composite members is developed that can be used for the eventual formation of design guides and procedures. *Communicated by P. Pedersen.

Partial interaction in composite steel and concrete beams with full shear connection

Abstract The maximum flexural capacity of composite steel and concrete beams with mechanical shear connectors and with full shear connection is usually determined from rigid plastic analyses. It is generally assumed in these analyses that there is full interaction and that the steel is fully yielded. In reality, there is always both partial interaction and an elastic zone of steel that will reduce the strength, but it is assumed that the beneficial effect of strain hardening will compensate. It will be shown that present design assumptions are generally safe for simply supported beams with mild steel sections but can become unconservative when dealing with composite beams with very strong steel sections, that is when the strength of the steel section (A s , f y ) is greater than that of the concrete section.

Size-dependent stress-strain model for unconfined concrete

The stress-strain behavior of concrete under compression, both in the ascending and descending branches, is crucial in determining both the strength and ductility of reinforced concrete members. This material property is generally determined directly from compression tests of cylinders or prisms. However, it is widely recognized that this material property depends on both the size and shape of the test specimen and the method of measurement. This paper shows that concrete deformation because of compression is both a material property and a shear-friction mechanism and that by taking both of these deformations into account it is possible to derive a stress-strain relationship that is size-dependent. This paper also shows how the stress-strain from cylinder tests of one specific length can be modified to determine the stress-strain relationship for any size of a cylinder. With this new procedure, the authors reanalyzed the results from 380 published tests on unconfined concrete to extract size-dependent strains at the peak stress and then used these results in existing curve-fitting models to produce size-dependent stress-strain models for unconfined concrete. This paper shows how these size-dependent stress-strain models can be used in a size-dependent deformation-based approach to quantify both the strength and ductility of reinforced concrete members.

The Gradual Formation of Hinges Throughout Reinforced Concrete Beams

ABSTRACT The rotational capacity of reinforced concrete beams is of funda-mental importance to the collapse of reinforced concrete structures. Research that started in the eighties used numerical approaches to simulate the rotational behavior using discrete and independent blocks encompassed by adjacent cracks. In this paper, these numerical approaches are taken a stage further. A numerical procedure has been developed that: allows for the interaction between the blocks along the full length of concrete beams; can cope with any number of layers of reinforcing bars; automatically predicts the occurrence of flexural cracks; and automatically allows for slip of the reinforcing bars.

Semi-compact steel plates with unilateral restraint subjected to bending, compression and shear

Abstract The buckling of thin-walled steel plates which are juxtaposed with a rigid medium must be treated as a contact problem, since the local buckles may only form away from the rigid medium in a unilateral mode. One particular example is the bolting of plates to the sides of reinforced concrete beams in order to stiffen and strengthen the original concrete beam. Plates which experience first yield before local buckling are referred to as semi-compact, and this paper uses an energy method developed elsewhere by the authors to study the unilateral local buckling of restrained plates, so that limiting depth to thickness ratios may be obtained that delineate the semi-compact section classification when the plate is subjected to a combination of bending, compressive and shearing actions. The application to retrofitting concrete beams is discussed.