Editor’s Note

The May 2006 issue of the Practice Periodical on Structural Design and Construction contains six papers. These papers cover a diverse set of topics, and each focuses on an interesting and informative practical area pertinent to design and construction. The variety of topics covered in this issue will be appealing to a wide group of readers involved in structural, geotechnical, and construction practices. Of special interest in this issue are two papers—one on design of barriers and the other on blast-load resisting capacity of reinforced concrete shear walls. These papers provide a good start in introducing certain aspects of building design as it pertains to homeland security. In addition to these six papers, structural design and construction forums are also included in this issue. Each forum covers a timely topic of particular interest to practicing engineers.

The first paper is presented under the title of “Mitigation of Soil Movements from Pile Driving,” by M. R. Svinkin. The main subject of this paper is on the soil displacement that is generated from driving piles. This displacement can affect surrounding structures and may impose damage to them. Among potential damage scenarios can be the compaction of granular soil under the foundation of the surrounding structures, which may eventually result in substantial soil settlement. The displacement generated from pile driving, according to the author, can especially be significant when the pile is driven in soft to medium clays. The paper explains several measures that can be used to mitigate the detrimental effects of direct structure vibrations, soil densification, and heave and settlement in clays. Vibrations generated from pile driving can impose a significant dynamic load on surrounding structures, affecting their integrity and serviceability. The paper provides an insight into the dynamic effect of induced vibrations, and the measures discussed in this paper provide readers with information on proven methods that can be adopted in practice to mitigate this effect.

The second paper published in this issue deals with controlling rock blasting methods deployed in urban areas. The paper is entitled, “Managing Rock Blasting Work in Urban Environments” and is written by G. F. Revey. The author starts the paper by introducing the areas where controlled rock blasting methods are used in practice. The author explains the significance of vibrations produced from rock blasting practices and further elaborates on how such an effect has become a subject of attention by nearly all parties involved including design engineers, blasters, regulators, project supervisors, and managers. In addition, the significance of the problem is stressed in terms of explosive security, storage and handling, overbreak control, and community relations, etc. The paper is unique and informative and provides an insight into the effects of rock blasting practice that would need to be considered in various stages of the project from planning to construction. The author further presents information on practical methods in managing blast practices, especially those that have been successfully implemented in urban areas. The practical methods introduced in the paper for mitigating the vibration induced by blast work are proven techniques and provide the readers with valuable information that can be considered in design and construction.

The title of the third paper is “Assessment of Potential Seismic Damage to Residential Unreinforced Masonry Buildings in Northern Illinois.” This paper is written by S. Khudeira and J. Mohammadi, of the Illinois Institute of Technology, Chicago. While it is widely believed that northern Illinois is a low-risk area for earthquakes, the authors explain that with the acceptance of certain risk levels, there is a potential for low seismicity in the area, with the possibility for moderate to significant damage to unreinforced masonry (URM) residential buildings. It is explained in the paper that damage to URM buildings can be estimated based on fragility curves available for this class of structures. A fragility curve presents the probabilities of occurrence of predefined states of damage versus the severity of the earthquake (which is often defined in terms of ground accelerations). Various states of damage, ranging from slight damage to complete collapse, are often depicted in a cluster of fragility curves. The paper explains the process of estimating a probable ground acceleration level at a given site based on a predetermined probability of occurrence using available data from U.S. Geological Survey web sites. Such data are based on past occurrences of earthquakes in the midwestern United States from sources such as the New Madrid seismic zone. Based on probable acceleration levels that can be experienced in northern Illinois and utilizing fragility curves, the authors arrive at damage states specific to URM residential buildings. Using the stock of URM residential buildings in northern Illinois, they arrive at estimates for the number of such buildings that can experience various states of damage. For example, the authors indicate that for a $50\text{-}\text{year}$ return period, the maximum acceleration for the area would be about 0.017g. This level of acceleration will cause slight damage to about 1% of buildings and nonstructural damage to about 4% of them. For a $500\text{-}\text{year}$ return period, the acceleration level is 0.057g. This will result in severe damage to about 1% of buildings, moderate damage to 5%, slight damage to 17%, and nonstructural damage to some 53% of URM residential buildings. Similar numbers for a very rare event corresponding to a $\mathrm{1,000}\text{-}\text{year}$ return period are also provided in the paper and the results are discussed. This paper is especially helpful to designers and planners in identifying the potential seismic risk involved with URM buildings and estimates for any property losses.

The fourth paper in this issue provides a discussion on innovative methods in accelerating the construction of a highway bridge. This paper is entitled, “Accelerating the Construction of a Highway Bridge in Ohio,” and is written by O. Salem et al. The paper explains that the methods proposed and implemented to accelerate the construction of a certain bridge was initiated by the Ohio Department of Transportation in an effort to build bridges faster and better. Specifically, the use of a precast, posttensioned slab bridge was considered instead of a cast-in place slab. The target time to complete this task was $16\text{days}$ ; however, the construction work was completed in $19\text{days}$ and was, nevertheless, considered successful in terms of construction time. Among the causes of delays were weather and equipment-related problems. The paper further explains that the coordinated effort between the contractor and the state transportation department was instrumental to the success of the project. Specific issues related to preparation for unexpected problems are discussed and mentioned as important considerations in the planning phase of a project. This paper is very informative and serves to point out the importance of implementing strategies that can be used in reducing construction time in areas where daily traffic must be restored without prolonged delays.

“Security Barrier Design” is the title of the fifth paper, with P. Terry and M. Tholen the authors. The paper explains the purpose of vehicle barriers as elements used to restrict vehicles from entering areas where they might cause injury to people or property damage. The authors explain that typically these barriers are small-diameter, moveable, closely spaced posts that are not designed for specific forces. The paper refers to the SEI/ASCE 7-02 document (published in 2002) as a source and suggests that a $\mathrm{6,000}\text{-}\mathrm{lb}$ lateral load may be used to design each barrier. According to the authors, the barriers are a hindrance to normal traffic; however, they are easily deformed and will not stop large errant vehicles or drivers who are intent on driving over them. The authors then go on to present a rational basis for determining a design force for security barriers. As explained in the paper, this design force is derived from rigid barrier impact acceleration values reported in the literature for vehicles with similar kinetic energy. With a growing interest in providing security to many public buildings by installing planters, bollards, and barriers, this paper is timely and provides readers with a good start for an introduction to the design of barriers as well as their design loads and performance.

The sixth paper is entitled: “Blast Assessment of Load-Bearing Reinforced Concrete Shear Walls.” This paper is written by C. J. Naito and K. P. Wheaton. The focus of the paper is in presenting a methodology for assessing the performance of structural elements subject to explosive loading. The method presented in the paper combines basic section analyses, equivalent single degree of freedom modeling, and static pushover analysis to calculate the blast resistance of an existing shear wall subject to an external explosion. The pushover analysis mentioned here is a procedure that simulates deforming the structure beyond its elastic limit, thereby computing the structure’s resisting demand. This method was used to identify regions that may be vulnerable to the load arising from an external explosion. The paper further explains that the second floor wall was identified as the location of failure and was modeled as a system, which includes the stiffness contributions of adjoining wall sections as well as a component with fixed ends. The authors develop pressure-impulse curves to quantify the blast resistance of the wall relative to various levels of damage. As with the previous paper, this paper is also informative in providing the readers with design issues relevant to areas where enhancing structural security is a major concern.

The structural design and construction forums and the six technical papers presented in this issue are certainly focusing upon topics that may require further investigations and discussions. Readers are invited to comment on any of these papers by means of discussions, introduce their experiences pertaining to the topics of these papers, or present alternative opinions and views, especially on the topics covered in the forums.