Practice Periodical on Structural Design and Construction

Wood–concrete composites are floor and deck systems, which are comprised of a concrete slab integrally connected to wooden beams beneath by means of a shear connector. Use of a shear connector can significantly improve a deck’s strength and stiffness (up to approximately 2 and 4 times, respectively) when compared to that of a nonconnected structure—resulting in a highly efficient use of materials. Sound and vibration performances, as well as fire resistance, are also improved when compared to timber floors. This paper discusses the structural design and use of wood–concrete composites in existing or new floor construction. A composite-mechanics analysis for semirigid shear connectors, taken from the European code for timber design (Eurocode 5), is described. It is further adapted to the allowable stress design method in the design of a commercial floor application using a high-performance glued-in shear connector system from Germany.

Analytical seismic responses of structures retrofitted using base isolation devices are investigated and the retrofit schemes are illustrated. The retrofitting of various important structures using seismic isolation technique by incorporation of the layers of isolators at suitable locations is studied. Three specific structures such as historical buildings, bridges, and liquid storage tanks are selected to investigate the effectiveness of the base isolation in seismic retrofitting. Different types of isolation devices, such as elastomeric bearings and sliding systems are evaluated for their performance in the retrofitting works. The response of the retrofitted structural system is obtained numerically by solving the governing equations of motion under different earthquakes and compared with the corresponding conventional structure without any retrofit measures, in order to investigate the effectiveness of base isolation in retrofitting of structures. It is observed that the seismic response of the retrofitted structures reduces significantly in comparison with the conventional structures depicting effectiveness of the retrofitting done through the base isolation technique. This paper also distinctively elaborates on the methods of construction in retrofitting works involving base isolation.

This paper deals with determination of actual design moment in the flexural design of ultradeep reinforced concrete rafts. Due to diagonal crack in concrete, the workpoint of the internal tension-compression couple resisting the applied moment is shifted by a distance equal to the effective depth of the member. This shift in the workpoint necessitates that the design moment at a particular section shall also be shifted accordingly. The case is highlighted with the example of a $9.0\mathrm{m}$ $\left(29.5\mathrm{ft}\right)$ deep circular raft that is acted upon by upward buoyant forces as well as downward gravity loads. Design moments in various regions of the raft increased by 1.3 to 248% after application of the moment shift rule described in the paper. The substantial increase in moment values signifies the importance of the phenomena for ultradeep reinforced concrete rafts.

The objective of this study was to use rapid visual screening (RVS) methods to identify potential seismic hazards for Oregon’s public facilities, including schools, hospitals, fire stations, police stations, and emergency response centers. There were 1,075 buildings screened in nine western Oregon counties. This study is part of a larger effort under the 2005 Oregon Senate Bill 2 to assess the seismic needs and upgrade public facilities in Oregon. RVS methodology generally followed FEMA 154 Rapid Visual Screening of Buildings for Potential Hazards: A Handbook. This method identifies structural type and building characteristics that may indicate poor performance under the maximum considered earthquake (MCE). Each building is given a final score related to the probability of collapse under the MCE. Screening was conducted by four individuals over three months. Quality assurance (QA) testing on nine buildings examined consistency between screeners. QA results showed final scores varied between screeners depending on building size, structure type, and architectural cladding. FEMA 154 was developed using California buildings. Differences between Oregon and California construction and the use of FEMA 154 in Oregon are discussed in this paper, reviewing the Uniform Building Code (UBC) and Oregon Structural Specialty Code (OSSC) amendments. The study provided two important conclusions. First, the average final score for buildings screened fell below the FEMA 154 cut-off score of $2.0\text{Second}$ , the OSSC had an exception to the UBC that allowed the construction of unreinforced masonry buildings two stories or less in height. With this context, screening results can help in assigning priorities for further analysis and seismic retrofits.

Wood composite I-joists have become an attractive option for floor joists in residential construction. One disadvantage of I-joists is the restrictions on hole size and the inability to notch the top compression flange. This technical paper evaluates two cold-formed steel reinforcers to strengthen I-joists that have been improperly cut—one to reinforce the top flange, and another to reinforce the web. The reinforcers were tested at various locations along the length of the beam. Based upon testing results, the notched I-joists with the flange reinforcers retained 60.2% of the strength and 77.0% of the stiffness of the original I-joists. The I-joists with the web hole and single-sided reinforcers retained 78.2%% of the strength and 95.7% of the stiffness of the original I-joists. I-joists with the web hole and the double-sided web reinforcers retained the I-joist strength and 95.1% of the stiffness of the original I-joist. These reductions in strength and stiffness can be used to determine if the reinforced I-joists are suitable for particular loading applications.