Practice Periodical on Structural Design and Construction

The Sheffield Brick and Tile Company produced a series of structural tile units that were used to construct floor and roof decks. The tiles were used as integral components in composite concrete, tile, and reinforcing bar deck systems. After roughly 40 years of service, the Sheffield Tile Deck System (STDS) in a school building failed. Investigation of the failure provided a clear indication that the design/development process overlooked a potentially critical feature of these systems. The investigation also revealed a mechanism whereby an STDS could provide adequate service, then fail in a rather abrupt fashion. During the investigation, reports of other STDS failures were discovered, including some referenced in Sheffield Brick and Tile Company correspondence to an owner of a STDS, suggesting he have it checked out by a qualified engineer.

This paper presents an efficient manual design approach, to obtain a near least-weight design by following prescribed procedures, for the preliminary design of long-span king-post steel truss systems. An innovative simplified analysis model is firstly established, and then the design requirements according to Canadian Standard on Limit States Design of Steel Structures (CSA-S16.1) and American Specification on Load and Resistance Factor Design are formulated. Design examples in North America are presented based on the proposed design procedures. The results of the study suggest that the proposed design method provide an efficient and practical solution for the preliminary design of long-span king-post truss systems.

The process of thermal degradation of wood products was reviewed in the context of the molecular constituents of wood—cellulose, hemicellulose, and lignin. Test data on $2\times 4$ lumber subjected to 66°C (150°F) for 48 months were reviewed, and the loss of strength as measured by modulus of rupture was reported to be 32%. The basics of heat transfer in attics were reviewed and test data on simulated attics in several locations were summarized. It was noted that thermal degradation is a cumulative process, dependent upon both temperature and duration of exposure. The effect of combined temperature and duration on potential thermal degradation of attic framing and sheathing can be minimized at the design stage by specifying light-colored shingles and roof details that provide for maximum attic ventilation. Through the use of a continuous soffit and ridgeline ventilation system, peak attic temperatures from solar radiation will be reduced and thus significant thermal degradation of attic framing and sheathing should be unlikely during the life of the roof structure.

The paper discusses a few issues related to capacity rating of existing bridges using field test results. The principles of proof and diagnostic load tests for capacity evaluation are presented through discussing the rating formulas for both tests. The proof load rating is proven a lower bound method. The diagnostic rating is proven the same as linear extrapolation, meaning an upper bound approach in nature. Two different methods used in the literature in calculating load distribution factors are discussed. The two methods are proven theoretically equal in an ideal case, but could be significantly different for field bridges due to the effects of many field factors. To distinguish the two methods, one is defined as load distribution factor (LDF) and the other as girder distribution factor (GDF). An example is used to demonstrate the discussions. The results indicate that, on one hand, the measured LDF, though calculated from measured strains, cannot fully reflect the capacity conditions of field bridges. It reflects only a relative load distribution among girders. On the other hand, the GDF approach may overestimate the bridge capacity, because it includes all the beneficial effects. Some beneficial effects may not be reliable for ultimate capacity and thus need to be removed from the capacity rating.

This paper, about the bridges built in Oporo during the 19th century, aims to pay a modest but justified tribute to three inspired engineers (Stanislas Bigot, Gustave Eiffel, and Théophile Seyrig) and their daring techniques and illustrious legacy. Let us hope that the scanty traces of their genius, excellence, and courageous efforts may serve as a stimulus to all those who are encouraged to foster such a noble art. For 115 years, Maria Pia Bridge, spanning the River Douro, provided a rail link between Oporto and Gaia, thus making a direct link possible between Oporto and Lisbon. It was an extremely daring bridge for its time; its arch had the greatest span in the world. In 1990, the American Society for Civil Engineers awarded it the International Prize for civil engineering works based upon of its unusual style. Lu$\acute{ı}$s I Bridge, built a few meters from the site of the old Suspension Bridge, comprises two decks supported by a large iron arch and five pillars. The arch is formed by two divergent parabolic curves, with a chord of 172 m and a rise of about 44.6 m. It still holds the record for the world’s largest iron arch.

Handheld computers are becoming more powerful and their application to construction projects is becoming increasingly feasible. Wireless connectivity allows handheld computers to access the Internet for Web-browsing and data transfer. Potential construction handheld computer applications include data collection, electronic books and reference materials, access to computer-aided design drawings, estimating, and scheduling applications. Mobile construction applications can be differentiated into two categories. They are general applications that can be used on many projects, and project-specific applications that must be tailored to a specific project. The capabilities of the two most popular handheld devices, the Palm and Pocket PC devices, are discussed and compared. The potential and costs of using handheld devices for Web access are discussed. A prototype Palm Web-clipping application is described. The capabilities of commercially available software packages and several prototype construction applications are discussed.