Modern Codes Of Practice Research Articles

Seismic Performance of Ordinary and Damage-tolerant Concrete Beam-column Joints under Reversed Cyclic Loading

The adoption of the capacity design principle in modern codes of practice allows for multi-storey frame structures to exhibit ductile behaviour in a major earthquake without collapsing. Whilst the risk of shear failure in regions of large inelastic deformation can be largely reduced, the detailing requirements in capacity design often leads to reinforcement congestion that adds difficulty during the construction process, due to the high amount of transverse reinforcement required to provide shear resistance and confinement. The work presented in this paper forms a part of a wider research programme that aims to simplify the detailing requirements of transverse reinforcement in the joint and plastic hinge regions of moment-resisting frame structures. To this end, damage-tolerant concrete known as engineered cementitious composite (ECC) was used to substitute concrete in these critical regions. In this article, the results of reversed cyclic tests on two half-scale exterior beam-column joints, constructed with ordinary concrete and ECC, are presented. Key features of the response such as the reversed cyclic hysteresis loops, stiffness degradation and cumulative energy dissipation are discussed, along with crack development under reversed cyclic loading in the form of digital strain maps.

Machine learning-based prediction of CFST columns using gradient tree boosting algorithm

Among recent artificial intelligence techniques, machine learning (ML) has gained significant attention during the past decade as an emerging topic in civil and structural engineering. This paper presents an efficient and powerful machine learning-based framework for strength predicting of concrete filled steel tubular (CFST) columns under concentric loading. The proposed framework was based on the gradient tree boosting (GTB) algorithm which isone of the most powerful ML techniques for developing predictive models. A comprehensive database of over 1,000 tests on circular CFST columns was also collected from the open literature to serve as training and testing purposes of the developed framework. The efficiency of the proposed framework was demonstrated by comparing its performance with that obtained from other ML methods such as random forest (RF), support vector machines (SVM), decision tree (DT) and deep learning (DL). The accuracy of the developed predictive model was also verified with the current design equations from modern codes of practice as well as existing ML-based predictive models.

A universal approach for evaluating earthquake safety level based on societal fatality risk

Residual risk exists in our buildings even if they were designed in conformance with modern codes of practice. Various approaches have been implemented or proposed in the last decade for setting risk-based performance requirements for seismic design of building structures. However, there is insufficient consideration about the aggregated risk for society, which could be significant especially for a densely populated metropolitan city. This paper introduces a rational and universal approach for evaluating the adequacy of structural safety requirements by comparing societal risk functions based on probabilistic loss assessment with a proposed regulatory requirement that aims to limit the mortality rate to “as low as reasonably practicable (ALARP)”. The proposed approach is then applied to Melbourne, Australia, in a case study, which shows that the earthquake fatality risk for the society appears to be unacceptable. The outcome can be used for justification of a seismic retrofitting policy or a required change of the design code level. The proposed scheme is also applicable to other natural hazards and for safety engineering applications generally.

First order reliability method on soil strength parameters estimation and stability analysis

The application of the first order reliability method (FORM) on the estimation of soil strength parameters and on the probabilistic analysis of slope stability problems is examined. Typical slope stability problems use the bi-parametric Mohr - Coulomb failure criterion and modern codes of practice (e.g. EC7) require some statistical measures for analyses purposes, either deterministic or probabilistic. Statistical approaches for the estimation of the measures of (a) the best estimate and uncertainty of these parameters (used in probabilistic analyses) and (b) their characteristic value (used in deterministic analyses) are presented herein. The uncertainty is estimated either by direct statistical methods or by application of the FORM, a methodology for uncertainty (via error propagation) calculation. Equations of uncertainty are derived for the direct shear- and the typical triaxial-test. An application of the FORM to the planar failure limit equilibrium problem is presented, which can be adjusted to the slices’ method. The reliability check with respect to the safety margin is preferable as it reduces the non-linearity effects, while the influence of cohesion uncertainty is more critical. A sensitivity check with regards to the uncertainties of soil parameter is recommended for probabilistic analyses.

On the Safety of the European Stability Design Rules for Steel Members

The European stability design rules for steel columns, beams and beam-columns are classically based on Ayrton-Perry formulations that rely on the calibration of imperfection factors in order to estimate the maximum resistance. More recently, “general approaches” have been proposed that combine in-plane and out-of-plane behaviour based on a single reference length. The safety of design rules in modern codes of practice is based on the use of partial factors and the separation of the uncertainty related to loading and resistance. EN 1990 - Annex D [1], for example, contains a procedure for the safety analysis of resistance functions, based on First-Order Reliability Methods. However, its application to stability design rules is not straightforward and several additional assumptions are necessary to ensure that a target probability failure is achieved. Finally, design rules and its accuracy depend on the accuracy of the relevant basic variables such as material properties, geometric properties and imperfections. It is therefore required to appropriately characterize the statistical distributions of these basic variables in order to comply with the (semi-) probabilistic safety level assessment of design rules. This paper discusses the different approaches for the derivation of design rules for columns, beams and beam-columns and proposes a mechanical consistent general approach. Secondly, a consistent procedure for the probabilistic assessment of the safety level of stability design rules is presented that simplifies the way material and geometrical properties are considered while maintaining its statistical relevance.

Modern Codes of Practice: What is Their Effect, Their Value and Their Cost?

Drawing on some 40 years experience with many aspects of structural code preparation and use, views are expressed on their purpose, production and presentation. Their role as part of the portfolio of advice and guidance employed by structural engineers is discussed and suggestions made to assist in securing the community’s acceptance of updated documents. While the content has been heavily influenced by the author’s direct experience—both in terms of the fields of expertise and the geographical regions in which that expertise has been gained—it is believed that many of the points made have a general value across all materials and structural types and in all areas of the world.

Testing and analysis of a traditional oak frame

Despite the widespread historical use of green oak framing, using all-timber connections, their engineering performance is poorly understood. Restoration of existing structures and design of new buildings are both often reliant on the skills of the carpenter and historical precedents. Structural engineers frequently struggle to validate green oak frame designs using modern codes of practice. The present paper presents findings from a study undertaken to investigate the structural performance of arched-braced green oak sub-frames. The sub-frames were part of a traditional roof structure in a barn that had fallen into disrepair and was to be replaced. To inform the design process and improve engineering understanding, five identical arched-braced sub-frames were commissioned for load testing under laboratory conditions to failure. The experimental results from the sub-frame tests, including deformation and load capacity, are presented. Experimental load capacities are compared with a novel collapse load analysis.

Evaluation of dynamic eccentricities obtained using a probabilistic approach, response spectrum methods and modern building codes

AbstractIn this paper a probabilistic approach has been adopted to study both the effects of uncertainty in earthquake frequency content and the correlation between earthquake frequency content and ground motion intensity on the response of a single‐storey torsionally coupled elastic structure. The earthquake ground motion has been assumed to be a Gaussian, zero mean, stationary random process which is fully characterized by a power spectrum. The ground acceleration power spectrum is idealized as a probabilistic normalized power spectrum computed from actual earthquake records. The advantage of such an idealization is that it enables the effect of the natural frequency as a controlling structural parameter in torsional coupling to be assessed. Comparisons of the dynamic amplifications of eccentricity with those obtained from modern codes of practice and conventional response spectrum analyses have been made.The results of this study have shown that the variation in the frequency content has a significant effect on the response of low frequency structures, while the correlation between the frequency content and the intensity of seismic ground motion is insignificant for the wide range of structures considered.The structure natural frequency has been shown to be an important controlling parameter in the torsionally coupled response of structures subject to seismic loading. The frequency dependence of the dynamic amplification of eccentricity was found not to be reflected in the response spectrum analysis and the torsional provisions of modern building codes.

A Detailed Appraisal Of The Strength Of TraditionalTimber Truss Eaves Joints

The structural engineer working on the refurbishment of buildings with traditional timber joints is often faced with the task of assessing the strength of the truss in its present condition, with possible damage or deterioration from years of service. Current practice is to avoid replacement or strengthening where possible (Hume, 1991). Modern codes of practice do not refer to the strength of traditional joints, and simple methods of equilibrium are unduly conservative. A study was undertaken to investigate the strength of two commonly occurring types of eaves joint, using both laboratory tests on scaled joints, and computational analyses of detailed stress distributions in the timber. Materials tests on the shear capacity of timber showed that the along-grain shear strength is not single-valued but is best defined by a Mohr-Coulomb model, and that measured values defining a shear envelope were considerably in excess of values recommended by British Standard 5268 (1990). The computational analysis indicated that the stresses along a plane of shear failure in an eaves joint was highly non-uniform. Close correlation was achieved between the failure loads of several scale model truss joints and detailed finite element analyses of stresses along and normal to the failure plane combined with the Mohr-Coulomb envelopes. Introduction For several hundred years, the construction of joints in timber roof trusses followed a traditional pattern based upon notches, tenons, laps, dovetails, Transactions on the Built Environment vol 15, © 1995 WIT Press, www.witpress.com, ISSN 1743-3509 286 Architectural Studies, Materials & Analysis scarfs and dowels (Harris, 1978, and Hewitt, 1980). The carpenter sized the timbers and selected the joint type and proportions by experience. No structural analysis was conducted, because the mathematical skills were not generally available, and the loads and timber strengths were completely unknown. Despite this situation, failures were rare because the timber sizes were chosen to be generous, and the craft guilds ensured apprenticeships for trainee joiners, so that safe practices were handed down. In addition, the requirement of adequate stiffness to limit deflections led to the use of heavy sections. In the present day, the structural engineer may need to assess, in building refurbishment, the factor of safety of timber trusses which have deteriorated with time, and which may be required to carry additional loads based upon modern Standards. BS 5268 Section 7.3 (1990), offers some guidance on modern stress graded timbers and gang nail joints, but this is a very different form of construction to the traditional roof truss (Yeomans, 1992). Two types of eaves joint became widely used in roofs of halls and larger houses, and are often to be assessed during refurbishment work. They are the simple notch (sometimes also dowelled, tenoned, or strapped), and the inclined notch (sometimes dowelled or strapped), see figure 1. While the loads impinging upon an eaves joint of a Victorian timber truss may now be readily calculated by the structural engineer, the strength of a notched joint is less definitive. A simple approach would be to assume a shear failure along the grain due to the horizontal component of the rafter force, resisted by an average shear strength of the timber. This, however ignores the detailed mechanics of the joint, and the complex pattern of stresses around the joint. Figure 1 Two types of eaves joint, and the plane of shear failure.