1995 Research Reports No R704-R719

Abstract

This paper presents a relatively simple procedure for assessing the magnitude and rate of development of settlements developed in a clay layer by an earthquake. A pore pressure generation relationship developed by Japanese researchers is utilised in a numerical consolidation analysis for this assessment.

For an idealised problem, the effects of earthquake magnitude on the excess pore pressures and settlements is examined. The influence of these pore pressures and settlements on short-term and long-term axial response of piles is examined. It is found that, if the Ritcher magnitude exceeds about 6, the earthquake-induced pore pressures and settlements in the clay may be significant, and pile performance may be adversely affected.

Abstract

An apparatus has been designed to study the underpinning and upgrading of footings by a pile at the centre. in this paper, each piece of apparatus for the footing and underpinning tests is described in detail, including the test vessel, cylindrical membrane system, model pile and footing, drainage and back pressure system, pile jacking and loading system, the instrumentation and data logging, and leakage tests. The results of the one-dimensional consolidation stage of tests, model footing tests, and underpinning and upgrading by piles will be published in the future papers.

Abstract

This research report describes a test programme conducted into the behaviour of cold-formed square hollow section (SHS) beam-columns of slender cross-section and follows an earlier research report into the behaviour of compact SHS beam-columns by the same authors (Sully and Hancock (1994)). The tests were conducted in a purpose built test rig capable of applying load and moment in a constant ratio. The test specimens were pin-ended specimens loaded at two different ratios of end moment. The maximum second order elastic moments are calculated from the maximum applied end moments, and the applied load. Comparison of these moments is made with the interaction design rules from AS4100 Specification (SAA (1990)) and the AISC-LRFD Specification (AISC (1994)).

Abstract

A series of tests on simply-supported channel and Z-section purlins screw-fastened to sheeting has been performed in a vacuum test rig. The purpose of the tests was the provide accurate non-linear response data for unbridged purlins, and purlins with one or two rows of intermediate bridging (bracing).

In this report, the lateral deflections and stresses determined in four of these tests are compared with those obtainedd from a non-linear, out-of-plan elastic analysis. This analysis incorparates a model which can be used to calculate the lateral deflections of, and stresses in, the unconnected flanges of both simply-supported and continous cold-formed steel channel and Z-section purlins screw-fastened to sheeting, and subject to either wind uplift or gravity loading.

Abstract

This report presents a superposition approach for studying the influence of bridging forces upon the opening of single and multiple cracks in elastic solids under mode I loading. The bridging forces may be purely elastic and proportional to the crack opening displacements, but an elasto-plastic bridging law is more likely to respresent reality in a fibre-reinforced solid. The fibres debond from the elastic matrix at a certain critical crack opening and thereafter provide a residual bridging force due to frictional pull-out.

From a mathematical point of view, the elasto-plastci bridging law introduces an additional (logarithmic) singularity at the point of discontinuity in the bridging force, besides the square root singularity at the crack tips. These singularities have been analytically isolated both for isolated crack and a doubly-periodic array of cracks, so that only regular functions are subjected to numerical integration.

The solution for an isolated bridged crack is also used to check the accuracy of the numerical procedure developed for multiple cracks. The double infinite summations necessary for their solution have been found to be divergent in earlier studies. The procedure developed in this report overcomes the problem of divergence and results in high accuracy.

The mathematical solutions are used to study the influence of varying amounts of fibre reinforcement upon the macroscopic response of two fibre-reinforced cementitious composites: a conventional fibre-reinforced cement and a high performance fibre-reinforced (DSP) cement.

Abstract

The in-plane inelastic strengths of steel arches are investigated using a finite element program for the nonlinear inelastic analysis. The elastic-plastic behaviour of the arches is determined by taking into account the effects of the arch curvature, large deformations, material inelasticity, initial crookedness and residual stresses. A number of different load arrangements are studied, which induce uniform compression or combined bending and compression in the arches. The effects of various factors on the in-plane inelastic strengths of steel arches are investigated.

Abstract

This research contains the results of a field survey of the application of quality assurance standards AS 3900’s series to three large construction projects in Australia. The study was conducted in 1994 in the University of Sydney’s School of Civil and Mining Engineering. It was preceded by an earlier and much wider study of the status of quality assurance in the Australian building and construction industry. An indepth analysis of the responses to a fairly large sample of people involved in the construction of three large construction projects has been carried out and included in this report. It has been found that the general approach to the imposition of quality assurance on industry was an ill-devised strategy; that the view from the construction pit on the usefulness of quality assurance is in marked contrast to the aims and objectives of quality assurance; that the communication processes within projects as well as the industry as a whole remain poor; that there is little evidence to confirm that the quality of the finished facilities are influenced by the application of the quality assurance; that the rank and file of the construction industry are not generally converted as far as embracing of the quality standards AS3900’s series is concerned.

Abstract

This report presents the results of a series of tests performed as part of an investigation into the behaviour and design of thin-walled I-sections in combined compression and minor-axis bending. A rig consisting of two interlinked actuators was used to perform tests on one type of cross-section loaded sequentially in compression and bending and proportionally with a moment gradient.

Tests have been performed to determine whether the behaviour of thin-walled I-sections in combined compression and minor axis bending is load path dependent. in these tests, the axial orce and the end moment were applied sequentially. The first method involved the application of the end moment before the axial force while in the second method the axial load was applied before the end moment. The moment gradient tests were performed to study the behaviour of thin-walled I-sections when the maximum moment is applied at the end of the specimen.

The results of the current series of tests are compared with the results of tests described in a companion report “Tests of Thin-Walled I-Sections in Combined Compression and Minor Axis Bending, Part II – Proportional Loading Tests”, where the beam-column behaviour was examined by applying axial force and equal end moments in a constant ratio. The present test series shows that sequential loading produces beam-column strengths that are greater than or equal to those obtained using proportional loading.

Abstract

There have been controversy and uncertainties surrounding the rotational behaviour of conservative internal bending moments in three-dimensional frames. The two contesting representations of conservative internal bending moments are the quasi-tangential and the semi-tangential moments, each of which has its own shortcoming from the purely physical point of view. This situation must be rectified as the correct identification of the nature of internal moments is indispensible for reliable buckling and large displacement analysis of three-dimensional structures, especially when they are subjected to externally applied moments or torques. This paper presents a new type of conservative moment which has hitherto never been considered in the literature, and demonstrates that the proposed representation of conservative internal moments can be justified on both physical and the rigorous mathematical grounds. Various issues relating to finite rotations and the work done by conservative moments in space are also addressed.

Abstract

The report describes a test program on cold-formed plain channel columns compressed between fixed ends and pinned ends. It is shown that local buckling does not induce overall bending of fixed-ended channel columns, as it does of pin-ended channel columns. A series of tests was performed on plain channel specimens consisting of two cross-section geometry’s fabricated from high strength steel by brake-pressing. Tests were performed over a range of lengths which involved pure local buckling, overall flexural buckling and flexural-torsional buckling.

The local buckling loads obtained from testing are shown to be in excellent agreement with theoretically determined local buckling loads. The different effects of local buckling on the behaviour of fixed-ended and pin-ended channels are investigated by comparing strengths, load-shortening, load-deflection, load-end-rotation and load-end-moment curves, as well as longitudinal profiles of buckling deformations. Detailed measurements of geometric imperfections and material properties were conducted.

Abstract

The report presents an experimental investigation into the test strengths and the behaviour of cold-formed lipped channel columns compressed between fixed ends and pinned ends. It is well-known that local buckling of pin-ended channel columns induces overall bending of the section. However, this phenomenon does not occur in fixed-ended channel columns which remain straight after local buckling until overall buckling occurs. Consequently, local buckling has a fundamentally different effect on the behaviour of pin-ended and fixed-ended channel columns. A series of tests was performed on lipped channels brake-pressed from zinc-coated Grade G450 structural steel sheets. Two different cross-section geometries were tested at various lengths which involved pure local buckling, distortional buckling as well as overall flexural buckling and flexural-torsional buckling.

The different effects of local buckling on the behaviour of fixed-ended and pin-ended channels are investigated by comparing strengths, load-shortening, load-deflection, load-end-rotation and load-end-moment curves, as well as longitudinal profiles of buckling deformations. Detailed measurements of geometric imperfections, material properties and residual stresses were conducted.

Abstract

This report describes a series of-tests performed on slender I-sections fabricated from high strength steel plates by welding. The objective of the program was to determine the section capacity for two different I-sections when subjected to compression and major axis bending. The Series I cross-section had slender flanges and a slender web both of which underwent local buckling, while the Series 11 cross-section had stocky flanges but a more slender web so that local buckling was confined to the web for this cross-section.

The tests were conducted in a purpose-built test rig capable of applying axial load and bending moment in a constant ratio. The tests were performed using different axial load to moment ratios, as well as pure axial load and pure moment, hence allowing the moment-axial force interaction curve to be constructed for the two cross-sections.

Detailed measurements of material properties, residual stresses, and geometric imperfections were performed prior to the tests. The test results are compared with the rules of the Australian Steel Structures Standard AS4100 [1,2], the American Institute of Steel Construction Load and Resistance Factor Design Specification [3], the British Standards Institution BS5950 [4], and Eurocode 3: Part 1. 1 [5].

Abstract

This report presents results of a series of tests performed as part of an investigation into the behaviour and design of thin-walled I-sections in combined compression and minor-axis bending. A rig consisting of two interlinked actuators was used to perform tests on one type of cross-section loaded in pure compression, combined compression and bending, and pure bending.

The test results are compared with the design strengths of the Australian Standard for Steel Structures AS 4100, the AISC Load Resistance Factor Design Specification, and the Eurocode 3 Part 1.1 Specification for the Design of Steel Structures. It is shown that the experimental interaction curve is close to being linear in the intermediate and long slenderness ranges. Thus, the tests support the choice of a linear interaction curve in AS 4100 and Eurocode 3.

The design interaction curves of the AS 4100, the AISC-LRFD Specification and Eurocode 3 are shown to be conservative in all cases, particularly in the high moment regions. The principal reason why these curves are conservative is attributed to the definition of the design bending section capacity are presented which are based on behaviour observed during the tests. The resulting moment axial force interaction curves are conservative and in reasonable agreement with the tests.

Abstract

In the assessment of the strength and stability of sway frames using “elastic” design, the modern trend in structural design specifications around the world (including the British Standard BS5950:Part1, the Australian Standard AS4100-1990, the Canadian Standard CAN/CSA-S16.1-M94, and the Eurocode3) seems to involve the use of “notional” horizontal loads, in conjunction with the assumption that the effective length of the columns in the plane of the frame is unity, the determination of second-order moments using an appropriate elastic analysis, and the application of a member strength interaction equation. Despite the seemingly widespread acceptance of the “notional load” approach as a rational design philosophy, there are inconsistencies and inaccuracies in the way the method is prescribed in the different specifications worldwide.

The notional load approach described above stands in contrast to the more traditional “effective length” procedure in which notional loads are not used and the axial strength component of the member strength interaction equation is computed using member, story or system buckling analyses. Current practice in the Load and Resistance Factor Design (LRFD) Specification of the American Institute of Steel Construction (AISC) for the in-plane strength design of columns and beam-columns in steel frames involves the calculation of effective length factors (K-factors) and the determination of second-order moments using an appropriate elastic analysis in conjunction with a member strength interaction equation. While the calculation of K-factors for the in-plane strength design of members in braced (non-sway) frames is relatively straightforward, there are a number of subtleties, complexities and different philosophies involved in the effective length procedures for unbraced (sway) frames. As well as being confusing to many designers, effective length calculations are often tedious and may tend to obscure the behavior of the real “physically imperfect” frame. This report explains the motivation for, the background to, and the calibration of the notional load approach in frame design. Although the report is primarily directed at investigating the applicability of the notional load procedure within the existing framework (i.e., the column curve and beam-column interaction formulae) of the AISC LRFD Specification, the majority of the concepts expounded and the conclusions drawn are applicable to structural steel design in the wider context.

Abstract

 The report derives a bifurcation analysis of members undergoing local buckling in the fundamental state. The members are assumed to be geometrically perfect in the overall mode but may include imperfections in the local mode. The overall displacements of the fundamental state are assumed to be small.

The theory is derived using variational principles. First, the variational equation for bifurcation of members with undistorted cross-sections is established. in order to show that the variational equation leads to the classical solutions for buckling of thin-walled members, it is applied to simple load cases, including singly symmetric members in compression and doubly symmetric members in combined compression and bending. Second, the variational equation for bifurcation of locally buckled members is established. It involves the stiffness of the member in the fundamental state. The bifurcation equation is applied to doubly symmetric cross-sections in compression, doubly symmetric cross-sections in combined compression and bending, and singly symmetric cross-sections in compression.

By using variational equations, the differential equations and boundary conditions for the fundamental and bifurcated states are derived. By solving the differential equations for the fundamental state, several phenomena characterising the behaviour of thin-walled sections are demonstrated.