Practice Periodical on Structural Design and Construction

Determining the most efficient and economical way to build a new or replacement bridge is not as straightforward a process as it once was. The total cost of a bridge project is not limited to the amount spent on concrete, steel, and labor. Construction activities disrupt the typical flow of traffic around the project and results in additional costs to the public in the form of longer wait times, additional mileage traveled to get around the work zone, or business lost attributable to customers avoiding the construction. The risk of injury to workers because of traffic interactions or construction activities increase with each hour spent at the construction site. Finding a way to shorten the time spent on the jobsite is beneficial to the contractor, the owner, and the traveling public. Prefabricating certain bridge elements reduces the time spent at the construction site and reduces the effects on the road users and the surrounding community. For example, steel beams with composite concrete decks reduce the construction time over cast-in-place concrete superstructures. In some instances, entire structures have been fabricated off-site under strict environmental and quality controls and then shipped to the site and erected in a matter of days instead of months. The total cost of using prefabricated bridge elements (PBE) depends greatly on the scale of the prefabrication. The more that prefabrication is used, the lower the costs. Even under limited use, however, prefabrication is usually comparable to traditional construction techniques. However, when durability and user costs are taken into account, the overall cost may be significantly less than traditional piece-by-piece construction. To improve the competitiveness of prefabricated composite bridges, a European research and development project, ELEM RFSR-CT-2008-00039, was started in 2008. The overall objective of the project is to make prefabricated bridges more competitive through development of new cost-effective, time-efficient, and sustainable bridge structures. The project has started with a knowledge extension, in the form of the workshop on “Composite Bridges with Prefabricated Deck Elements.” This workshop was held in Stockholm, Sweden, in March 2009 to share the knowledge and experience gained by agencies around the globe. During the workshop, experiences from Europe and the United States were presented in an effort to promote the use of accelerated bridge construction (ABC) and prefabricated bridge elements.

A common approach to estimating the point of fixity is to utilize the results of a single pile lateral analysis. Although no universal agreement exists as to the definition of the location of the point of fixity, it is generally accepted that its location will affect the computed stresses and displacements of a bridge structure. This study summarizes a method to determine a cantilever’s equivalent length of drilled shaft foundation elements supporting a bridge. Results from an equivalent frame model are compared to those for bents modeled using the finite element method and nonlinear soil models for three bridges in North Carolina. Results indicated that the equivalent frame model provides responses that are comparable to those obtained from more rigorous finite element analyses. The study presents the results of the optimization of the support system by reducing the number, or size, of the shafts while maintaining an acceptable level of safety.

The existing wood-diaphragm-to-masonry-wall connections in unreinforced masonry (URM) buildings provided very little or insufficient resistance in past earthquakes. Recent strengthening techniques for the connections between URM walls and flexible diaphragms concentrate only on the installation of wall anchorages for out-of-plane tension forces and shear bolts for in-plane shear forces. Strengthened chord elements, however, are also essential parts of URM buildings to resist earthquakes. This paper proposes seismic rehabilitation techniques where steel angles are used as chord reinforcement. A practical design example is presented, where chord axial forces caused by in-plane diaphragm deflections and chord shear flows caused by transverse seismic forces are computed. The computed axial forces and shear flows are to be used in the design of the chord reinforcement and the chord shear connections, respectively.

Inelastic mechanisms leading to failure in interior reinforced concrete beam–column (RCBC) connections, designed on the concept of strong column–weak beam philosophy, primarily result from failure of the joint region and yielding of longitudinal reinforcement in beams. In this manuscript, two novel easy-to-use probabilistic methodologies have been developed that can determine with sufficient accuracy the occurrence of either of these inelastic mechanisms leading to failure, given the geometric, material and loading parameters of an experimental investigation. One model was developed by using the relevance vector machine method, a machine learning methodology that uses a Bayesian formulation and results in a sparse representation. Another model was binomial logistic regression, which can relate the qualitative event of inelastic mechanism resulting in failure initiation with several experimentally obtained independent parameters. It can also quantify the relative importance of each of these independent parameters. Both methods show good predictive efficiency and can be utilized by a designer, engineer, or researcher to obtain a preliminary probabilistic estimate of inelastic mechanisms that lead to failure of interior RCBC connections. This manuscript also presents comparative evaluations of utilizing these two models.

The structural design of a three-story building in Palmela, near Lisbon, Portugal, is analyzed. Because of architectural constraints, the main facade of the first floor was designed in a setback of the second floor, which created a 13.0 m (42.6 ft) span between supports. To comply with deflection requirements a Vierendeel girder was projected between the second and third floor slabs. Taking advantage of the reduced size of the structure and therefore low computation demand, two nonlinear analyses were conducted. To account for the effect of creep in the construction phase, a physically nonlinear analysis was performed. Furthermore, the second-order effect on the vertical elements was accounted for through a geometrically nonlinear analysis. The nonlinear analyses allowed for a more slender and cost-efficient design when compared with values obtained from the traditional abacus to account for viscoelasticity.

Rafter pairs are regularly employed in timber buildings, partially because they may be supported in a wide variety of ways to achieve the various objectives of the designer. A detailed examination of seven common rafter configurations with varying support conditions is presented. The results of detailed structural analyses as well as evaluations of the impacts on roof system performance are discussed so that designers can weigh the relative advantages and disadvantages of their selections.

For walls of great dimensions, fall protection is problematic. Reinforcing steel erectors have to climb on the reinforcement bars to anchor and position themselves to do their tasks and to protect themselves against falls. Two problems are identified: (1) the selection of a harness and positioning and fall-arrest equipment and (2) an anchor point sufficiently strong for the positioning and the personal fall-arrest systems. This paper describes the dynamic fall tests that have been carried out to verify the strength of tied reinforcement used as an anchor point for the fall-arresting and positioning systems of reinforcing steel erectors.