Practice Periodical on Structural Design and Construction

Conservative restoration principles developed for the protection of monuments are currently applied in the structural upgrading of traditional existing buildings in order to preserve their cultural heritage. Timber structures, typically, present in these buildings to support roofs and floors, had for long been substituted when buildings were upgraded, often using new and different materials, and sometimes yielding unsatisfactory results in terms of structural behavior. The current conservation trend requires developing criteria for interventions and implementing operative procedures complying with modern structural safety requirements and satisfying conservative restoration principles. Research progress is also being made in understanding the behavior of traditional timber joints and elements in service conditions and at the limit state under exceptional actions, as well as the effectiveness of different types of reinforcement. Actual cases of restoration of buildings that included conservation of the timber structures have proven to be economically competitive with the choice of substitution.

Precast concrete panels offer a means whereby a road can be closed, reconstructed, and reopened with minimal inconvenience to the motoring public. The use of such panels is a very viable and cost effective Portland cement concrete pavement reconstruction solution for repairing short lengths of distressed pavement that does not justify the mobilization of paving spreads or where closures cannot be of such duration to accommodate long curing times. Additionally, by casting the panels in a fixed facility it is possible to increase quality control of the pavement’s mix and casting. Three construction scenarios are described here to illustrate the effect project work site constraints have on construction operations when precast concrete panels are used to reconstruct a busy roadway.

Seismic screening, evaluation, and rehabilitation design of two existing wood-framed structures are performed using FEMA 154, FEMA 356, ASCE/SEI 31, and the 1997 UBC. FEMA 154 screening demonstrates the importance of examining construction drawings. Plans revealed a structural deficiency, but screening alone indicated no further evaluation is needed. Demand-to-capacity ratios for shear walls and roof diaphragms are examined. 1997 UBC design provisions for new buildings are not necessarily conservative compared to FEMA 356 rehabilitation guidelines. Also, FEMA 356 and 1997 UBC design provisions are not necessarily conservative compared to existing building evaluation in ASCE/SEI 31. A likely cause of the unexpected results is the conservative linear static procedure and associated $m$ factors for wood in FEMA 356 and ASCE/SEI 31. Research is needed to better calibrate these factors and acceptance criteria to account for duration of shaking, number of cycles of nonlinear behavior, and redundancy.

The down-aisle lateral load-resisting systems of pallet-type steel storage racks are, typically, frames utilizing special beam-to-column moment-resisting connections. The behavior of these connectors is poorly understood, and consequently, there is significant uncertainty as to proper values of connector stiffness and strength to use in design. This technical note presents the results of down-aisle shake table tests performed on steel pallet-type storage racks fabricated from cold-formed sections and incorporating two different teardrop beam-to-column connector systems. This study is a follow up on a previous experimental investigation on bolted beam-to-column connectors by the same authors. The main objectives of the tests were to determine appropriate static load connector rotational stiffness values from measured dynamic characteristics of storage racks under low-amplitude vibrations. The experimental results indicated that the beam-to-upright-connector stiffness values reduce with excitation amplitude. While the connector stiffness decreased significantly during the most intense shaking, it recovered almost all of its initial values at the completion of each test. Unlike the bolted connections, the stiffness recovered immediately without the need for low-level white-noise excitation to “settle in” the connector prior to full recovery of the initial stiffness.