Bridge Construction Equipment: An Overview of the Existing Design Guidance

Abstract

The present paper concerns bridge falsework structures, highlighting the current challenges associated with their design and giving indications of how they can be considered. Despite being the most critical stage of a structures' lifetimemost failures occur during construction rather than after projects have been completedthe design and use of temporary structures are not usually treated as carefully as in the case of permanent structures, and thus do not receive the same level of research attention and research funding. This is clearly evidenced by the number and the state-of-the-art level of existing standards and guidance documents concerning permanent structures as opposed to temporary structures, such as bridge falsework structures. Therefore, there are difficult challenges in their design when compared with the design of permanent structures, for instance: Generally, the design of bridge falsework structures is controlled by the self weight of the permanent structure, by second order effects resulting from displacements in the temporary structure, or by the changement of their supporting conditions, in the case of movable falsework systems, during the construction of the permanent structure. As a result, these temporary structures are subject to load values close, or even above, the assumed design values during almost their entire service period, whereas permanent structures are designed for load values that have a small probability of occurring during their design lifetime; Bridge falsework structures are used for brief periods of time, although their sum could represent 15 years or more. Some design philosophies, based on the temporary nature of these structures, specify smaller safety factors than the ones used in the design of permanent structures. However, since the ratio between their cost and the cost associated with their collapse is much lower than for permanent structures, this methodology needs to be reconsidered using a risk-based approach. Furthermore, the use of smaller safety factors may underestimate the loads and lead to unsafe structures; Bridge falsework structures are assembled, (re)used for short periods and dismantled several times. Additionally, erection, inspection and maintenance procedures are often found to be inadequate. As a result, construction errors are likely to occur, i.e. the human factor is always present with potential severe consequences. Permanent structures are currently assembled only once and used for large periods of time and they exhibit a much higher degree of inherent robustness against human errors; Due to their repeated reuse , bridge falsework structures face during their design period several different exposure conditions to various hazard scenarios in a number far greater than any permanent structure needs to be designed against; Finally, bridge falsework structures due to their purpose are generally light and slender structures, and therefore their performance is more sensible than permanent structures to errors during their erection and use, and to inadeq...

Evaluación de un sistema de andamio móvil en condiciones de uso temporal

“…The latter situation is applicable to standardized ancillary elements, reused for the construction of different permanent structures. In this frequent case, the continuously changing temporary construction stages might imply higher uncertainties associated with actions, resistances and the models used for analysis than those for the permanent structures [1,12,13]. This in turn would mean that higher target reliabilities and partial factors should be adopted for the design of the temporary structures, in spite of their aforementioned comparatively lower likelihood of exposure to extreme events.…”

“…However, some risk acceptance criteria are always needed in structural engineering. A consistent approach for temporary structures is currently lacking, being one of the consequences that the associated reliability levels exhibit large variation and are often smaller than those corresponding to permanent structures [13]. A need for a coherent framework and guidance for design of temporary construction equipment is identified including the choice of appropriate target reliability levels [14].…”

Risk‐Informed Requirements for Design and Assessment of Structures Under Temporary Use

“…The observable relatively large failure rate of temporary structures, with important consequences in many cases, suggests that the implicitly admissible risks associated with such structures or activities might be too high in relation to generally accepted risk levels corresponding to permanent structures under persistent situations, referring to conditions of normal use within a time period of the order of the design working life (EN 1990(EN , 2002. André et al (André, Beale, & Baptista, 2012a) support this statement by affirming that due to a lack of a consistent approach in current design codes, the reliability levels associated with temporary structures exhibit a great variation and are often smaller compared to permanent structures. Indeed, for the time being the current codes and standards do not provide a coherent framework for design or assessment of structures under temporary use and there is a need for guidelines with respect to the choice of appropriate target reliability levels (Caspeele, Steenbergen, & Taerwe, 2013).…”

Learning from incidents during bridge erection

“…Indeed, as noted earlier, many of the temporary activity-related problems that must be dealt with in everyday bridge construction are more elementary [1] and often associated with the sort of human error not usually envisaged in design codes and standards. André et al [8] summarise the findings of a survey conducted by Matousek and Schneider [9] on the causes of damage in different types of structures. Most of the types of damage identified in the 800 cases reviewed occurred during the construction phase and were primarily attributable to carelessness, ignorance or insufficient expertise.…”

“…An example given in [12] illustrates the importance of such considerations, showing that the number of diagonal braces required to assure the stability of support scaffolding may not be accurately determined unless knowledge is available on the behaviour of the connecting joints between braces and standards. In everyday practice, given the general want of specific standards for bridge construction equipment [8] (with an occasional exception, such as [13]), ancillary equipment designers often resort to codes and standards intended for permanent structures, structural engineering principles and best practice. Nonetheless, the aforementioned considerations on the specific behaviour of ancillary equipment are a clear indication that standard rules for permanent structures may not suffice for the design and analysis of such equipment.…”