Practice Periodical on Structural Design and Construction

Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

The direct tension pull-off test has gained popularity as a test method used in the laboratory and especially in the field to assess the quality of bond between externally bonded fiber-reinforced polymer (FRP) repair materials and concrete owing to its low cost and simple procedure. However, the small scale and localized nature of the test can lead to high variability in the results. Furthermore, the test does not load the bond in a way that is representative of service conditions. Because of these limitations, satisfactory interpretation of results can be difficult. This paper examines the challenges that may be encountered when analyzing the data obtained during testing, including the high variances. Past research efforts using pull-off tests, and results of recent field and laboratory testing by the authors, are discussed to evaluate the benefits and weaknesses of pull-off tests as a quality control and research tool. The authors conclude that pull-off tests have many drawbacks, and if they are used, great care is needed in their application. It is recommended that if this method is to be used as a quality control procedure in the field, pull-off tests on the concrete alone should be conducted to obtain baseline values, and supplementary tests such as acoustic sounding also be used. For laboratory conditions, it is advised that alternative testing procedures be considered and large sample sizes be used to make statistical validation possible.

AASHTO specifies a one-bolt-diameter cutoff for standoff distance to consider bending stresses in anchor bolts. When evaluating the strength of anchor bolts in accordance with these specifications, many cantilever-type support structures with a standoff distance of slightly more than one bolt diameter were determined to be structurally insufficient. In this paper, a comprehensive study on bending stresses of anchor bolts for cantilever-type structural supports was performed. Two finite-element models were developed, one using solid elements to model individual anchor bolts and the other using beam/plate elements to model an entire group of anchor bolts with a base plate. Parametric studies were carried out to investigate the effects of number of bolts, base plate thickness, and standoff distance on bending stresses. Based on ultimate strength theory, strength limit states for individual anchor bolts and entire groups of anchor bolts were derived to include the influence of local bending stresses. As an illustrative example, anchor bolts of an existing cantilever sign structure were evaluated in accordance with AASHTO and AISC. This example demonstrates advantages of the load and resistance factor design method over the allowable stress design (ASD) method.

Fiber-reinforced polymer (FRP) bridge decks have been increasingly used in both rehabilitation and new constructions because of their many advantages. However, the design process is not in a code format, and individual decks and bridges are designed on a job-by-job basis. The development of standards and guidelines is needed to promote wider acceptance of FRP decks. Extensive research has been conducted by the authors and collaborators on modeling, optimization, and stiffness and strength evaluations of FRP decks; shear connectors for FRP deck to steel girders; and bridge system concepts, in terms of both experimental investigations and analytical solutions. Based on these research findings, this paper proposes a set of design guidelines considering the strength of the FRP deck subjected to out-of-plane compression, out-of-plane shear, and bending; static and fatigue strengths of the deck-to-girder shear connector; and effective flange width of the bridge system. A design example is provided to illustrate the use of the proposed design guidelines.

Approximately 75% of deaths attributed to earthquakes in Latin America are caused by the collapse of heavy buildings. Hence, it is necessary to study new technological alternatives for structural systems to be used in 1-story housing units that are able to withstand seismic forces. Such structural systems must also be otherwise durable in nature as well as lightweight and moderately priced. The prefabricated system presented in this paper is made of self-supported panels (polyurethane foam and steel decking sheets—materials traditionally used for nonstructural elements), and it is currently being considered as part of a structural system for use in 1-story houses. During the last 10 years, several laboratory tests have been done to the panels to assess their materials and connections. According to the results, the panels display excellent promise, mainly from their demonstrated characteristics of low weight, high relative stiffness, and good performance of connections. These results further suggest that, when located in areas where the seismic risk is high, one-floor constructions incorporating these self-supported panels could withstand earthquakes generating spectral accelerations of $\text{>}3.0g$.

To mitigate concrete sulfur storage pits deterioration, it is important to understand the mechanisms leading to concrete deterioration. The Claus chemical process is the industry standard for obtaining sulfur from hydrogen sulphide gas (derived from natural gas). The deterioration of concrete pits can be from both environmental factors and chemical effects of the Claus process. This may take the form of corrosion, sulfation, acidic attack, thermal expansion, or polymerization. Corrosion occurs as a result of sulfuric acid formation. Reactions occur because of Claus products presence, ingress of water through the concrete matrix or from leaks in steam coils. Sulfation occurs mainly from catalyzing some of Claus products by concrete or its admixtures. An acid environment lowers the pH value of the concrete and leads to impacting the passive film protecting the reinforcing rebars. Effects of thermal expansion and polymerization are also discussed in this paper. Selection of the proper materials is crucial in the construction of a durable sulfur pit. Low porosity concrete prevents ingress of gas/liquid species inside the concrete and hence mitigates destructive chemical reactions inside the structure. Cementious materials that will lower the diffusion of gas and liquid such as silica will improve the durability of the sulfur pits. In addition, because of the pozzolanic reaction associated with the use of silica fume the Ca(OH) content will be reduced. Concrete with mineral additives such as silica fume will result in higher compressive strength, lesser permeability and higher corrosion and sulfate resistance. To assure the structure durability, designers need to understand and envision the operational conditions of sulfur pits. Utilization of wrong materials and construction practices can significantly shorten the expected service life of sulfur pits. Finally, repair of deteriorated sulfur pits needs also to be evaluated and conducted by specialized personnel. This repair can take many forms and scenarios including crack repair, structural members repair, durability liner, and structural liner. A proper strategized and engineered repair should be implemented to ensure the repair’s effectiveness and durability.

To protect the nation’s surface waters from sediment-laden discharge, the proper selection, design, application, installation, and maintenance of erosion and sediment control practices on active construction sites are imperative. These practices will be required to comply with new, stricter regulations applied by the EPA to control high sediment concentrations of storm water discharge from construction sites. One mean of controlling sediment-laden discharge is through the use of sediment basins. The purpose of this paper is to report results from a survey conducted to determine the state of the practice for sediment basin design, construction, maintenance, and inspection techniques used by state highway agencies (SHAs) nationwide. The survey consisted of 68 possible questions in six categories: (1) background and experience, (2) design, (3) construction, (4) maintenance of sediment basins during construction, (5) inspection and monitoring, and (6) lessons learned. A total of 37 responses (74% response rate) out of 50 SHAs were received and analyzed. The summary of the survey, including lessons learned, allows knowledge and experience to be transferred to practitioners that may have little or no experience with using sediment basins on construction projects. The survey shows that the typical design life of a sediment basin is between 6 months and 2 years; the generally accepted minimum storage volumes among most agencies is $252\hspace{0.17em}{\text{m}}^3\text{/ha}$ ($\mathrm{3,600}\hspace{0.17em}\text{cu ft/acre}$) of disturbed area draining to the basin, and 13 agencies use flocculant additives to enhance the efficiency of sediment basins.

The strategy for dealing with the blast-induced threats against a structure requires attention from planning and design stages, as introducing or altering various blast response mitigation strategies becomes either difficult or impossible later on. Blast response mitigation strategies can be incorporated in the structural design at concept stage, leading to a well-designed and -constructed structure that can exhibit improved blast resistance and at the same time maintain its architecturally appealing appearance. This requires knowledge of (1) intelligent strategies in the form of blast source isolation strategies or using advanced engineered materials, (2) material behavior under such loading, and (3) postexplosion functioning of the structure and its elements. In this paper, various strategies for blast mitigation are reviewed and discussed with an emphasis on presenting a comprehensive assessment of blast response mitigation technologies beginning from the necessary discussion on fundamental aspects of blast-induced impulsive loading and material characterization, especially at high strain rates. Apart from describing functioning of the commonly adopted measures, emphasis has been laid on the mechanics of the sacrificial blast wall and design using various materials used for its construction.

When properly designed, framed, and anchored, blast-resistant laminates for curtain walls can greatly reduce or eliminate the hazard and injury from flying glass, and are capable of maintaining the integrity of a building envelope and reducing interior damage in an explosion event. Existing blast-resistant glazing research and design practice ignores the negative phase of the shock wave, which can affect the response of a curtain wall system and anchorage. Therefore, dynamic modeling and high-explosive field testing of two full-scale curtain wall systems using a shock tube are presented in this paper. The LS-DYNA numerical simulations were verified using the blast testing of two curtain wall systems, an original design and a blast-retrofitted design. The response of the glazing system to the positive and negative phases was investigated. The modeled dynamic response correlated well with the measured response of the glass laminates and the mullion supporting the curtain wall units. This study can be used to improve existing methods and to provide affordable design recommendations for curtain walls under blast.

The engineered nature of metal plate–connected wood trusses may not be well understood by installers and other trade professionals, which can result in installation errors. Truss manufacturing, handling, and installation specifications are included in national design standards and truss misinstallation is therefore a code violation. Through use of the Delphi method, an expert-validated inspection methodology was developed by interviewing code officials, home inspectors, and truss manufacturers. The results included (1) identification of truss installation errors most likely to occur, (2) best practices for inspection methods, (3) determination of authoritative documentation, and (4) validation of the research methods. The inspection should begin at the top of the structure and move in a circular, systematic pattern downward through each level, and should concentrate on the identified high-risk aspects of truss installation. Installation problems include the following: broken or cut webs and chords; damaged, offset, loose, or missing gusset plates; bracing; bearing; leaning and bowing; cantilevers; hanger hardware; and temporary repairs.