D.K. Bull

Multispring Hinge Element for Reinforced Concrete Frame Analysis

AbstractThis paper describes the development and validation of an analytical multispring plastic hinge element that can predict elongation of ductile RC plastic hinges together with its flexural and shear responses. The element consists of layers of longitudinal and diagonal springs that represent the behavior of concrete, reinforcing bars, and diagonal compression struts. Beam tests reported in the literature, for which elongation of plastic hinges was measured at different stages of the lateral cyclic loading, were used to validate the effectiveness of the newly developed plastic hinge element. Comparisons of the analytical predictions with experimental results show that the proposed element predicts elongation of plastic hinges satisfactorily. The ability of the model to predict elongation of a plastic hinge together with its flexural and shear deformations offers a significant advancement in seismic performance assessment of RC structures.

Slab Effects on Beam-Column Subassemblies - Beam Strength and Elongation Issues

This paper describes the effect of composite slabs in increasing beam strength and its implications for design. It also discusses the “beam-growth” phenomena, which can detrimentally influence the performance of a frame with reinforced concrete or precast concrete beams, and its impact on steel beams with RC slabs. From the subassembly testing conducted the slab increased the beam strength by around 40%. However the slab could not maintain strength at large drifts without degradation with transverse or longitudinal decking placed around the columns. This indicates that while transverse or longitudinal slabs should not be considered in design to size the beam, they should be considered in the beam overstrength calculations for the design of other members. Also, both rational considerations and experimental results

Analytical Methodology to Predict the Beam Overstrength Considering the Composite Slab Effects

The design strength of moment resisting steel frames in seismic regions around the world is generally calculated without considering strength enhancement caused by the slab. For column and panel zone design in New Zealand, the beam overstrength including the slab effect is considered. If the slab could be detailed to provide reliable lateral force resistance, then considering it directly in design would result in smaller beam sizes and more economical steel frames. In this paper, a simple analytical model (considering all key modes of failures) to predict the variation in strength due to the presence of the slab is proposed and validated with the experimental data. The proposed model to develop dependable slab contributions may change the design of steel moment frames around the world.

Floor Diaphragm In-Plane Modelling Using Elastic Truss Elements

Different methods to model building floor diaphragm in-plane stiffness with truss elements are compared to identify the method most suitable for analysis in design. The methods considered include (i) an elastic diagonal truss element model, and (ii) an elastic diamond truss element model. The truss elements were placed in square blocks and are compared with FEM in terms of stiffness and capturing beam axial forces. It was found that diagonal model transferred some part of diaphragm force directly to the column. The diamond framework superior because it was less sensitive to mesh size, gives a more accurate stiffness with a lower number of elements and a more accurate beam axial force. Furthermore, it better provides information in a better format for design.

Beam Web-Side-Plate Connection Axial Performance

A number of beam web side plate connection configurations are analyzed under monotonic axial force. Parameters investigated include (i) gravity loads causing a beam shear up to 60% of the capacity, (ii) column lateral drift, (iii) beam lateral restraint along the length, (iv) packing effect represent the practice when plates do not align perfectly, and (v) cope length. For the analyses conducted, gravity shear forces up to 0.6 times of the cleat plate gross shear capacity, reduced the connection compressive axial strength by up to 15% compared to connections without gravity loads. The connection axial strength varied by 10% with lateral drifts of up to 2% and the increase or decrease depended on the relative directions of drift and axial force. Also, axial strength of double-coped WSP connection decreased linearly with increasing the cope length. Other parameters were found to have less than 2% effect on the web side plate axial strength. A general simple design method to assess axial strength of these connections is proposed.

Seismic Testing of the Slotted Beam Detail for Reinforced Concrete Structures

This paper describes the development of the slotted beam detail. The design, construction, testing and results of two large experimental programs investigating the seismic performance of the slotted beam detail, described herein as Phase I and II, are presented. In Phase I a two-storey, two-by-one bay, reinforced concrete slotted beam superassembly was tested under quasi-static cyclic loading. The specimen was designed, constructed and erected to closely replicate New Zealand construction techniques for a typical multi-storey building, which enabled the practicality of the detail to be assessed. A demanding biaxial loading protocol was applied to enable performance assessment of the slotted beam connections. In addition, the threedimensional interactions between structural elements in the lateral load resisting system were examined. In Phase II five three-dimensional exterior beam-column subassemblies with floor slabs were tested under a similar regime to Phase I. Two subassemblies were directly extracted from the superassembly tested in Phase I and tested to determine the residual capacity of the subassemblies, following a large earthquake. The tests on the remaining three subassemblies investigated viable options for, and performance of, repair retrofit solutions for reinforced concrete slotted beam connections following large earthquakes. The retrofit solutions utilised tension-compression yielding, sliding friction and lead extrusion external energy dissipation devices. The tests also served to assess the performance of the replaceable dampers for new build

DESIGN CONCEPTS AND APPLICATIONS OF HIGH-STRENGTH CONCRETE IN NEW ZEALAND

An overview is presented on New Zealand applications and design concepts for the utilization of high strength concrete (concrete compressive strength greater than 55 MPa (8,000 psi)) in various forms of structures that are required to withstand seismic loading. In order to take advantage of the high concrete compressive strengths and enhanced durability designers and researchers are investigating various structural applications. The performance of elements of these structures ranges from remaining elastic during a major seismic event through to being required to exhibit significant ductility in the major events.