Editor’s Note

This issue of the Practice Periodical on Structural Design and Construction includes a Structural Design Forum article, four papers, a discussion and closure of a previously published paper.

The Structural Design Forum by Mohammadi deals with “Wood Porch Design and Construction Issues.” This article was prompted by the June 2003 porch collapse in Chicago where more than 50 individuals were crowded on the second and third levels of a back porch together with beer kegs and similar party items, resulting in the collapse of the porch. In this incident, 12 individuals were killed and 57 were injured. In August 2007, the court ruled the owners liable for the porch collapse. This article describes effective porch design. Its purpose is to initiate a discussion among structural engineers on porch design issues such as design load magnitudes, materials and acceptable connection details, and connection hardware.

The first paper in this issue entitled, “Restoration and Strengthening of Timber Structures: Principles, Criteria, and Examples” is by Parisi and Piazza. This paper deals with the application of conservative restoration principles, previously developed for the protection of monuments, to historically important timber structures as well as historic structures containing timber columns and other timber support systems. This includes understanding the behavior of traditional timber joints and other connection elements, and making certain that these function safely under contemporary use conditions and safety requirements. This paper should be of interest to architects and engineers working in the field of historic preservation of structures involving timber.

The second paper deals with “Pavement Reconstruction Scenarios Using Precast Concrete Pavement Panels.” Schexnayder et al. state that 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 reconstruction solution to repair short lengths of distressed pavement that do not justify mobilizing a great deal of equipment, or where road closure durations, cannot accommodate long curing times. Three construction scenarios are described to illustrate the effect project work site constraints have on construction operations when precast concrete panels are used to reconstruct a busy roadway.

The third paper in this issue deals with wood framed structures and is entitled, “Seismic Screening, Evaluation, Rehabilitation, and Design Provisions for Wood-Framed Structures.” In this paper by Baxter et al., seismic performance of two adjacent existing wood-framed structures is compared using several methods. The structures are portions of a school built in the mid-1960s. Classrooms and gymnasium are structurally separate but connected by hallways. Approaches compared include: FEMA 154, Rapid Visual Screening of Buildings for Potential Seismic Hazards; FEMA 356, Prestandard and Commentary for the Seismic Rehabilitation of Buildings; ASCE/SEI 31, Seismic Evaluation of Existing Buildings; and the 1997 Uniform Building Code. Results are compared and discussed.

The fourth paper in this issue entitled “Experimental Stiffness of Pallet-Type Steel Storage Rack Tier Drop Connectors” is by Filiatrault et al. The down-aisle lateral load-resisting systems of pallet-type steel storage racks are typically frames using special beam-to-column moment-resisting connections. The behavior of these connections/connectors is poorly understood, and thus there is a fair amount of uncertainty as to proper values of connector stiffness and strength that should be used 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 tier drop beam-to-column connector systems. The primary objective of the tests was to determine appropriate static load connector rotational stiffness values from measured dynamic characteristics of storage racks under low amplitude vibrations.

The discussion by Springfield and closure by Khudeira and Mohammadi included in this issue are that of the paper entitled, “Assessment of Potential Seismic Damage to Residential Unreinforced Masonry Buildings in Northern Illinois” authored by Khudeira and Mohammadi.

We invite our readers to present discussions on some or all papers of this issue.