No abstract

Like other competitive bridge erection techniques, incremental launching is a highly vulnerable process that entails considerable risks to persons. In steel and composite bridges, in particular, patch loading and other mechanisms that induce instability must be avoided. Considerable uncertainties are associated with both resistances and support reactions during launch operations due to the broad range of factors involved. Nonlinear finite element (FE) analysis is very useful for the explicit verification of both local and overall system stability during steel structure launching. Monitoring, in turn, may be a very powerful tool for reducing the risks associated with such operations. Further research is needed both to establish safety levels for temporary structures and on-site activities and to develop a suitable design format for nonlinear FE analysis. However, in everyday practice, engineers and builders must deal with much more basic problems, often related to the interaction between the structure under construction and the ancillary resources used, as exemplified in the case study described in this contribution. The lessons learnt from such incidents are extremely useful for improving the strategies presently in place to reduce construction-related risks.

Due to its severely damaged condition, former La Laguna cathedral was demolished and rebuilt between 1905 and 1913, saving only its neo‐classical façade. Reinforced concrete, at the time an innovative technology, was deployed to expedite construction and reduce costs. The trade‐off for these benefits was the risk associated with the use of a scantily understood material. Although a reliability‐based assessment of the corrosion‐damaged load‐bearing system showed that structural safety requirements were fulfilled for the future service life, less than 100 years after its reconstruction, the temple was so profoundly deteriorated that the roof had to be replaced entirely. Reconstruction began on the healthy part of the existing columns, underneath the capitals. The solution adopted retains the geometry of the 1913 structure, while improving its ventilation and lighting as well as its aesthetics by reconfiguring the proportions as nearly as possible to the golden ratio. The ribs in the vaults and main dome, characteristic of the neo‐gothic style of the building, were built with self‐compacting concrete, reinforced with glass‐fiber polymer rebars, and joined monolithically to the shells, as well as to the existing walls and columns. The 0.08 m thick shells are also made of a relatively unknown material, self‐compacting concrete reinforced with polypropylene fibers. In order to reduce to acceptable levels the uncertainties associated with innovative technologies, in addition to laboratory tests, a full‐scale prototype of a typical dome was constructed prior to the execution of the new roof. Nearly a century after the previous, negative experience, thanks to modern structural engineering and materials science, new challenges can be assumed.

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.

<p>Since the successful translation of many constraints into an aesthetically appealing as well as reliable, functional and cost-effective structure is primarily a question of sound conceptual design, the importance of this step in the design process as a whole cannot be overstated. Nonetheless, the growing complexity of analysis and verification methods, materials technology and construction procedures is driving ever greater specialisation against a backdrop of increasingly extensive and opaque standardisation and control systems. Such specialisation comes at the expense of conceptual design training in engineering schools and consequently of structural engineers’ creativity and other skills necessary to create compelling designs for structures. The rules for ensuring robustness reflect the increasing complexity and opacity characterising structural design codes. While the practical importance of designing and building robust structures is universally acknowledged, the codes presently in place are often vague or confusing. Cross-referencing, in turn, may lead to loops around rules that, confounding engineers, are counterproductive. At the same time, however, that lack of clarity may afford opportunities for innovative solutions by building items that ensure robustness into the conceptual design of a structure. This paper proposes an operational design process that deals appropriately with all factors of structural performance, including robustness, without compromising bridge economy or elegance. That process, which combines several robustness strategies, including risk- based considerations, is illustrated with a case study.</p>