C.H. Yu

Testing of steel-concrete composite connections and appraisal of results

Abstract This paper presents results obtained from tests carried on six full-scale composite beam-to-column joints. The steelwork connection consists of a flush end plate welded to the beam end and bolted to the column flange. The steel beam section and concrete slab remained identical for all six specimens. Three types of column are used: bare steel, partially encased and fully encased columns. Other variables include the area of reinforcement in the slab and the presence of stiffeners in the column web. Moment–rotation curves obtained from the tests are compared with those predicted by an analytical model. Plastic analysis of cross section is used to develop the analytical model for the prediction of moment capacity. A simple spring model for the slab combined with that of the steel joint model, as proposed in Revised Annex J of EC3, is used to assess the stiffness of the composite joints. Generally, the proposed model can predict the moment capacity of composite joints with good accuracy. However, the model tends to over predict the rotational stiffness.

Testing of semi-rigid unbraced frames for calibration of second-order inelastic analysis

Abstract This paper examines the behaviour of semi-rigid unbraced frames through a series of tests on a variety of rectangular frames as well as their joints so that the analysis and design methodology can be developed and verified against the test results. The frame and joint tests employed similar beam and column sizes and had the same connection details. The two types of connections studied were top-seat-double-web angle and extended end-plate. Column-base connections were also included in the studies. Load-displacement plots are presented for all the test frames subjected to gravity loads applied to the beam and columns, and a horizontal load applied at the beam level. The principal objective of the joint tests is to provide a comprehensive set of moment-rotation data, in terms of stiffness and moment capacity, so that a comparative assessment of the frame performance due to the different connection types could be undertaken. Detailed descriptions of test arrangement, load sequences, test methods and data acquisition techniques are given. The general observed behaviour is discussed. Results from the frame tests are compared with the corresponding theoretical results obtained from a second-order inelastic analysis.

An economical structural system for wind and earthquake loads

Abstract An economical structural system which would mitigate undesirable vibrations due to wind and earthquake loads is being developed. In this proposed system, the inherent hysteretic damping of the knee–brace-frame (KBF) with shear yielding knee is tapped to maintain the structural integrity in the event of a severe earthquake, while the frictional damping (in the form of slotted bolted connection, SBC) in the brace of KBF is utilised to dissipate energy in order to meet the serviceability requirements during severe wind storms or moderate earthquakes. As SBC dissipates energy without causing permanent damage, part of the strength required for serviceability design can be reduced by activating the SBC at an appropriate slip force. This would economise the material required for serviceability design.

Stability of frames with semirigid joints

Abstract This paper presents a modified stiffness matrix method for finding the elastic buckling load of semirigid frames. The method, besides accounting for the partial rigidity of the joints, also considers the effects of flexure on axial stiffness, geometric changes and the P-Δ effect. An experimental test has been devised to check the validity of the theoretical analysis and it is found that the method gives results of reasonable accuracy. A computer program has been written to carry out the doubly iterative process of finding the buckling load and is used to make a parametric study on the effect of rigidity of various joints and also bracings on a single-bay double-storey frame. The results of the parametric studies are presented in charts.

OPTIMIZATION OF PRESTRESSED CONCRETE BRIDGE GIRDERS

This paper presents an application of generalized geometric programming to the optimal design of a prestressed concrete box bridge girder. The actual cost of construction consisting of prestressing. formwork and concrete is minimized. Constraints are formulated as stipulated by the British Code of Practice CP110. The constraints of the geometric program relate to bending and shear stresses, and geometric criteria. A sample design is presented and sensitivity studies are performed to test the influence of major design parameters on cost factors.

Stability of semi-rigid space frames

Abstract This paper presents a modified stiffness matrix method for obtaining the elastic buckling load of semi-rigid space frames. This is an extension of the method applied to semi-rigid plane frames. Again the method, besides accounting for the partial rigidity of the joints, also considers the effects of flexure on axial stiffness, geometric changes and the P-Δ effect. A computer program has been written to carry out the doubly iterative process of finding the buckling load. A parametric study on the effect of rigidity of various joints and also bracings on a single-bay single-storey space frame is made. Also, a space frame, simulating a simple scaffold, is studied for the effect of the rigidity of the bracings for three cases of loadings. The results of the parametric studies are presented in the form of charts.

Uniformly loaded rhombic orthotropic plates supported at corners

Abstract An approximate method to predict the bending behaviour of rhombic orthotropic plates supported at corners and subjected to uniformly distributed load is presented. The theory is based on the principle of minimizing the total potential energy and uses a polynomial deflection function. The analytical results predicted by the proposed solution are compared with those obtained by an established finite element package. In general, polynomial solutions and finite element values of deflections and stress resultants are in reasonable agreement.

An application of geometric programming to structural design

Abstract This paper presents an application of generalised geometric programming to an optimal design of a modular floor system, which consists of reinforced solid concrete and voided slab units supported on steel beams. A function representing the cost of the floor system in terms of design variables, length, width and thickness of components, and other engineering and cost parameters is minimized subject to various constraints depending on stresses and deflections. A dual-based algorithm has been used for solving the design problem. Analyses are performed to determine the changes in the optimal values of the design variables with respect to the changes in imposed loads on the floor system.

Collapse behaviour of sway frames with end-plate connections

Abstract A test program consisting of 10 frame specimens loaded to collapse at the National University of Singapore as part of the broad investigation on “analysis and design of semi-rigid frames” has been completed and briefly reported in Liew et al. (1997). This paper provided the details of three test specimens and describes the test observations of the sway frames under the combined actions of gravity and lateral loads. The load–deformation responses of the test frames and their connections under sequential and non-sequential loading are determined and compared with theoretical predictions. The moment–rotation characteristics of such connections are determined so that advanced analysis can be carried out and compared with the test results to determine if the ultimate load carrying capacity and load–deflection characteristics of such frames can be predicted by the proposed analysis method. This paper focuses the discussion on three of the frame specimens constructed using extended end plate connections. Comparison of test results with second-order refined plastic hinge analysis and Eurocode are made using the moment–rotation characteristics of individual beam-to-column connections established through tests.

Corner supported isosceles triangular orthotropic plates

Abstract The aim of this study is to investigate the bending behaviour of an isosceles triangular orthotropic plate supported at comers and subjected to uniformly distributed load. An approximate method using a polynomial deflection function together with the principle of minimizing the total potential energy is proposed. The analytical results predicted by the proposed solution are compared with those obtained by an established finite element package. In general, polynomial solutions and finite element values of deflections and moment stress resultants are in satisfactory agreement and the accuracy of the proposed method is thus established.