Practice Periodical on Structural Design and Construction

Pile installation into the ground by impact or vibratory hammers produces soil movements which may affect surrounding structures with major dynamic impact on adjacent buildings. Vibrations from pile driving may cause direct vibration damage to structures and compact granular soils with subsequent substantial settlements. Significant soil displacements occur during pile driving in soft to medium clays. Several measures can be used to mitigate detrimental effects of direct structure vibrations, soil densification, and heave and settlement in clay soils.

In recent years, controlled rock blasting methods have been used to excavate rock in shafts, tunnels, and chambers at many projects at urban locations throughout the United States. For engineers, blasters, regulators, project supervisors, and managers, controlling blast-induced vibrations and air overpressure and other risks associated with this blasting is becoming an ever increasing challenge. For urban work, explosives security, storage and handling systems, overbreak control, impacts of blasting on green concrete, community relations, and the availability of skilled labor also influence the outcome of the work. This paper presents practical methods regarding blast design and risk management practices that have been used successfully at high-exposure projects located in or near Boston; Atlanta; Portland, Ore.; Milwaukee, Wis., and other cities in the United States. Special focus is on practical blast design techniques that mitigate blast-induced vibration and air overpressure generated by shaft and tunnel blasts. Controlling blasting impacts on concrete of varying age and placement condition is also discussed.

Ground acceleration estimates for northern Illinois are used to assess any damage that can occur to unreinforced masonry (URM) residential structures as a result of potential future earthquakes. These estimates are based on probable future activities in the New Madrid Seismic Zone and are published by the U.S. Geological Survey for exceedance probabilities equal to 0.10, 0.05, and 0.02 per 50 years. Accelerations corresponding to higher exceedance probabilities (1.0 and 0.25 probability in 50 years) are obtained from simplified seismic hazard analyses. Damage is estimated based on fragility curves available for URM buildings. The probability of damage is then used along with the inventory of buildings to arrive at estimates of the percentage and the number of buildings that may suffer damage of various levels (ranging from nonstructural damage to total collapse). The study shows that considering $p=1$ exceedance probability in 50 years (i.e., a 50 year return period), the maximum acceleration for the area will be about $0.017g$ . This acceleration causes slight damage to about 1% of buildings and nonstructural damage to about 4% of them. With an acceleration of $0.057g$ , about 1% of URM buildings will experience severe damage, 5% moderate damage, 17% slight damage, and 53% nonstructural damage. This acceleration is based on $p=0.1$ exceedance probability in 50 years. A very rare event at $p=0.05$ exceedance probability in 50 years corresponds to $0.101g$ acceleration and may cause collapse in about 1.5% of buildings, severe damage to 4%, moderate damage to 16%, slight damage to 42%, and nonstructural damage to 84% of URM buildings.

The Ohio Department of Transportation (ODOT) created Strategic Initiative Number 9 to “build bridges smarter, faster and better.” One project undertaken by ODOT was to use a precast, post-tensioned slab bridge in place of a cast-in-place slab. To accommodate school schedules and a festival, the bridge was to be completed in 16 days. However, the bridge was actually completed in 19 days. Delays were due to weather, equipment problems, and confusion over plans and specifications. Contributing to the success of the project was the effective partnering between ODOT and the contractor, along with a high level of upfront planning. However it is necessary to address problems such as the lack of contingency plans and some unexpected issues that were overlooked in the planning phase.

After a brief introduction on vehicle barriers in general, the writers present a rational basis of determining a design force on security barriers. The design force is derived from rigid barrier impact deceleration values culled from published literature on vehicles with similar kinetic energy. The Appendix provide a summary of references for further study.

In this paper a methodology for assessing the performance of structural elements subject to explosive loading is presented. The method combines basic section analyses, equivalent single degree of freedom (SDOF) modeling, and a static finite element pushover analysis to calculate the blast resistance of an existing shear wall subject to an external explosion. The method optimizes the breadth of results while minimizing the calculation complexity required. A static pushover analysis is conducted to identify regions of vulnerability. The second floor wall is identified as the location of failure and is modeled as a system, which includes the stiffness contributions of adjoining wall sections, and also as a component with fixed ends. Pressure–impulse curves are developed to quantify the blast resistance of the wall relative to various levels of damage. The component model is found to underpredict the blast resistance by 7% when compared to the system model for impulsive demands. Simplified energy methods are also shown to bound results of the SDOF resistance curves.