Search

The relatively high failure rates, with important consequences in many cases, suggest that the implicitly acceptable risk levels corresponding to temporary civil engineering structures and activities might exceed the bounds of normally acceptable levels associated with different societal activities. Among other reasons, this may be attributed to the lack of a rational approach for the assessment of risks associated with the different technologies supporting these activities in general, and for structures in particular. There is a need for establishing appropriate target reliability levels for structures under temporary use taking into account specific circumstances such as reduced risk exposure times. This issue is being addressed in this article. Acceptance criteria for building‐structure‐related risks to persons obtained in prior studies are adapted to the special circumstances of nonpermanent risk exposure. Thereby, the general principle followed is to maintain the same risk levels per time unit as for permanently occupied buildings. The adaptation is based on the statistical annual fatality rate, a life safety risk metric that allows for a consistent comparison of risks across different societal activities and technologies. It is shown that the target reliability indices taking account of the temporary use of buildings might be significantly higher than the values suggested for permanently used structures.

Trabajo presentado en el Joint fib-RILEM Workshop Modelling of Corroding Concrete Structures, celebrado en Madrid (España), los días 22 y 23 de noviembre de 2010, The growing interest in upgrading existing reinforced concrete structures or extending their service life, and in ensuring greater durability in new designs, has led to a need for resistance models that take deterioration processes into account to verify structural safety. Bond activation between reinforcing steel and concrete is of cardinal importance in this context. A number of experimental studies have been conducted in recent years on bond failure, which normally leads to brittle behaviour. The findings have diverged rather widely, however, due primarily to differing test conditions. The present paper presents an experimental programme for eccentric pull-out tests in which specimens were subjected to both accelerated and natural corrosion in an attempt to surmount these inconsistencies. It also introduces an embedded fibre-optic sensing system with corrosion-resistant fibre Bragg grating sensors and discusses some of the findings.

With the growth and ageing of the stock of existing structures, structural assessment and retrofitting are fast acquiring a significant role in the construction industry. The benefits of upgrading existing reinforced concrete (RC) structures or extending their service life and of ensuring greater durability in designs for de novo construction have led to a need to include deterioration as a factor in structural safety models. Bond between reinforcing steel and concrete is of cardinal importance in this respect. The present paper proposes a unified formulation for assessing bond strength in corroded and non-corroded steel bars, and an associated model to accommodate the effect of transverse pressure where appropriate. The formulation is the result of applying multiple linear regression analysis to a database built from the findings of over 650 bond tests on corroded and non-corroded reinforcing steel reported in the literature. The data collected include a wide range of variables affecting bond strength, such as bar diameter, concrete compressive strength, concrete cover, anchorage length, confinement ratio and cross-sectional loss. A number of statistical criteria are used to compare the proposed formulation to the other bond strength assessment models, including the fib Model Code 2010 proposal for corroded steel bars. Further to the statistical tests conducted, the model proposed can be usefully applied to assess the structural safety of corroded RC members.

Bridge building entails considerable risk, as attested to by the relatively frequent occurrence of worksite accidents. In the accident reported on here, an overhead gantry derailed during the construction of the last of 13 spans on one of two nominally identical parallel bridges composing a precast concrete girder viaduct. As no prior anomalies had been detected, the structure was the object of a detailed forensic inquiry. The most likely hazard scenario was inferred from the mutually reinforcing findings gleaned from numerical calculations, experimentation, eyewitness accounts, and reconstruction of the accident sequence. Organizational flaws such as less-than-optimal interfacing and data exchange among the actors involved in viaduct construction were observed to be among the major underlying causes. The study showed that effective quality-assurance strategies, fluent worksite actor intercommunication, and a clear definition of tasks and responsibilities are of cardinal importance in preventing accidents.

Most building design codes distinguish structural reliability levels in terms of failure consequences, for which they normally define consequence classes based on building type and use. Although readily applicable in everyday practice, that approach may entail adopting inconsistent safety requirements. Such a significant drawback could be minimised by establishing separate reliability levels for key members on the grounds of the potential consequences of their collapse. Further to those concerns, this paper proposes a series of consequence classes determined in keeping with the number of persons at risk in a given collapse scenario and the extent of the respective damage. Consequence class-related models for predicting loss of life are derived from statistical assessments of data on over 150 collapsed buildings. The models developed estimate the number of fatalities and conditional probability of death of building users under given collapse circumstances. In addition to their utility in establishing target reliability values, these models can be applied in risk analysis of specific building structures, especially where the potential consequences of failure are high.

Many key aspects of bridge design are governed by site-related, geometric, functional and constructional constraints. Economy is yet another decisive factor in public works, whilst enhanced...

The assessment of an existing structure to determine its suitability for present and future use entails different sorts of problems than encountered when designing new structures. The differences revolve essentially around the nature of the information available. In existing structures, deteriorated or otherwise, the accuracy of the models used for such assessments can usually be improved by acquiring more data. The most accurate way to find actual load and resistance would be to conduct a probabilistic analysis using site data. This is a time-consuming process, however, calling for a working knowledge of probabilistic methods that may not be suited to everyday use by practising engineers. For this reason, in the past few years various studies have been conducted to develop assessment approaches, compatible with Eurocodes, which include the same verification format as normally applied for designing new structures. In this paper, the application of several of these approaches is illustrated by means of the reliability verification of one of the main beams of the reinforced concrete structure of an industrial building from the 1940s, recently transformed into a cultural centre. The obtained results are discussed and compared to the findings of a full probabilistic analysis.

Civil construction is a highly uncertain endeavour that entails a considerable risk, as attested to by the succession of incidents and accidents reported the world over. The reasons for this situation need to be identified before strategies can be adopted with a view of reducing the construction-related risks. Taking the forensic investigations of a series of accidents as a starting point, this article explores the generally applicable lessons learnt from those case studies. Such surveys show that the problems to be dealt with in everyday practice are rather elementary and often attributable to human error. Basic principles and recommendations are therefore put forward for the design, erection and use of temporary structures in general and ancillary equipment for construction processes in particular, aimed at reducing the risks associated with such activities. Moreover, as there is no general consensus on reliability requirements for the temporary structures, this paper addresses the establishment of acceptable life safety risk and the associated reliability levels. The requirements put forward aim to ensure the same statistical fatality rate per unit of time as for the permanent structures. The effect of the established principles, recommendations and requirements on the design and assembly of the temporary structures is illustrated by means of an example.

The courthouse at El Ejido has a trapezoid floor plan (47 m x 55 / 26 m) and comprises two distinct volumes that are structurally connected at basement level and by footbridges on the upper storeys. A third trapezoid unit featuring a glazed curtain wall façade cantilevers 8 m off the main façade of the front volume. This façade is a structural diaphragm wall, constituted by nine rows of vertical precast concrete members separated by horizontal cast-in-place, self-compacting concrete chords. The location of the courthouse in a seismic area and the short number of horizontal supports for the façade make this wall potentially vulnerable. The particularly high risk during construction called for careful planning based on a detailed analysis of the interaction between the structure and the ancillary resources used to build it.

Bridge building is a highly uncertain endeavour that entails considerable risk, as attested to by the succession of construction-related incidents and accidents recently reported in Spain and elsewhere. While efforts are being made to improve on-site safety, many issues are still outstanding, such as the establishment of reliability requirements for the ancillary systems used. The problems that must be dealt with in everyday practice, however, are more elementary and often attributable to human error. The overall organisation of the use of bridge construction equipment is in need of improvement. Close cooperation between the bridge engineers responsible for construction planning and ancillary element suppliers is imperative, for flawed interaction between building equipment and the bridge under construction may generate structural vulnerability. External quality assurance should likewise be mandatory.