Practice Periodical on Structural Design and Construction

Repair costs of reinforced concrete structures exponentially grow with the time from construction to the onset of corrosion and deterioration, up to inspection, evaluation, repair, and rehabilitation. Therefore, the planning of an automated-monitoring system, which is able to reveal the corrosion risk of steel reinforcement and other embedded items in concrete structures would be a critically important issue. If concrete structures such as a highway bridge are ignored from regularly planned structural condition surveys, inspections, and evaluations then it could lead to catastrophic failure and loss of life and commerce. Such failures of structures also may lead to significant financial liability. The corrosion potential of steel, whose change could indicate the onset of conditions favorable for corrosion initiation, can be monitored by embedding electrodes in the structure, either for measuring the start of corrosion or simply as a baseline reference for future inspection and evaluation. Judiciously selected suitable locations of these embedded electrodes depend on the type and geometry of the structure, as well as on the exposure condition of each of its critical structural elements. A computerized system has been in use in Italy for few years. The applications described here are for concrete structures, including one steel structure that is exposed to the sea-breeze on the Adriatic Coast of the City of Ancona, Marche, Italy. The system monitors and documents by means of the embedded electrodes and sends the records to a computer via a communication line data points both for the structure and the weather. The collected data on the computer are saved on backup files, analyzed, and finally sent via modem to a monitoring station for further processing and dissemination to the architect, engineer, and owner. This structural monitoring procedure has been applied to several concrete structures that are continuously controlled and managed from the monitoring station. These experiences show the effectiveness of the continuously monitored computer system for inspections and evaluations, as well as for scheduling repairs and rehabilitations. It is important to evaluate the installation of such a structural monitoring system on any infrastructure to minimize the impact of its disruption on public safety, daily commerce, future liability, and maintenance.

Commercial vehicle weight limits here refer to those on the gross weight, axle spacing, and axle weights. They have a notable influence on the deterioration and lifespan of highway facilities such as pavements and bridges. A new methodology is presented here for estimating the monetary impact to a network of highway bridges due to commercial vehicle weight limit increase. This methodology focuses on four categories of cost impact: (1) life reduction due to fatigue of steel components; (2) life reduction due to fatigue of reinforced concrete decks; (3) requirements for addressing deficiency of existing bridges; and (4) capacity requirements for new bridges. For illustration, an application example of the new methodology is presented. The results show that Categories 3 and 4, additional inadequate bridges and increased requirements for new bridges, contribute more significantly to the total impact cost. In addition, a computer software program for the methodology has been developed and is introduced in this paper to facilitate implementation. It is intended to be used for highway planning at different network levels, such as for state, provincial, federal, or national jurisdictions.

Crossframes in horizontally curved steel I-girder bridges are primary members. They must be designed for strength and fatigue. Curved girder analysis computer programs typically compute crossframe member forces only due to curvature effect; they do not calculate the crossframe forces due to wind and centrifugal forces. These forces must be calculated separately and combined with the curvature-effect forces using appropriate group combination load factors. If the crossframe forces from computer programs are suspicious, engineers can use hand procedures such as V-load method to verify these results. Also per current AASHTO Guide Specifications for Horizontally Curved Steel Girder Highway Bridges, when the girders are allowed to be analyzed neglecting curvature, the crossframe forces may be determined using the V-load method or other rational means. Using V-load method to find crossframe forces can be time consuming and mistakes are easily made. In this paper, a general solution to determine the end shears and end moments on crossframes in horizontally curved steel multi I-girder bridges is developed by V-load method. In addition, the end shears and end moments on crossframes are tabulated for 2-girder through 8-girder system. A design example for a 5-girder system is selected for demonstration.

A roofing system consists of a waterproof membrane, attachments, cover board (if present), insulation, and vapor or air barrier [retarder (if present)]. A roof assembly is a roof system that includes the structural deck. Wind-uplift ratings are reported by subjecting roof assembly mockups to wind dynamics. Most of the time, technical reports clearly document the properties of membranes and attachment systems (fasteners, plates, and seams) and only briefly mention the strength of the fastener-deck interface. Research by a North American roofing consortium established at the National Research Council of Canada, the Special Interest Group for Dynamic Evaluation of Roofing Systems, has demonstrated the significant influence of fastener-deck parameters on the wind-uplift resistance of mechanically attached roofs. This paper presents data and information from this ongoing investigation. Seven different roofing assemblies using three widely used roofing membranes with different fastener-deck combinations were constructed and tested under dynamic wind conditions. Assembly responses were measured based on two design factors: pressure and force. The present study identified three parameters characterizing the fastener-deck interface strength: deck grade, deck gauge, and fastener type. The study found that assemblies tested with steel decks having thicker gauge or higher yield strength tend to have greater fastener-deck strength and therefore they sustain higher wind-uplift pressures compared to assemblies with thinner gauge or lower yield-strength decks. Similarly, assemblies where the membrane attachment is made with fasteners with larger shank diameters sustained higher wind-uplift pressures compared to assemblies installed with smaller shank diameter fasteners. This study also found that fastener pullout resistance could be used as a verification factor for estimating assembly wind resistance.

Developing and constructing oil sand megaprojects are huge technological, engineering, and construction achievements for Alberta and Canada. Thousands of engineering and project management professionals and workers are contributing to the current effort with great pride and sense of satisfaction. But recent large capital oil sands construction projects have all experienced significant cost and schedule overruns. There are a number of reasons for these overruns. This paper provides a definition of a “megaproject,” illustrates the challenges in delivering oil sands megaprojects, and lists a number of reasons for cost and schedule overruns.

The international roughness index (IRI) was developed in 1986 to generate a longitudinal roadway profile analysis tool for asphalt surfaces. The IRI is typically applied to freeway and rural highway facilities where uninterrupted spans of asphalt are expected. The city and county of Denver (CCD) in cooperation with the University of Colorado Denver have examined the application of the IRI to urban roadway facilities. Elements of urban roadways that influence IRI values include drainage infrastructure and cross-street access. This paper details the equipment and methodology used to address challenges in assessing urban constructed roadways with the IRI. Repeatability studies were completed using five different inspectors involved in the data collection activities. The results indicated that repeatability varied between different inspectors by approximately 2%. A before-repair and after-repair study was completed on newly resurfaced roadways around the CCD in an attempt to establish a set of baseline values for the application of the IRI to urban roadways. The IRI values for a sample of 23 test cases showed a weighted average postpaving improvement of approximately 36%. Recommended urban IRI values for good and acceptable surfaces are suggested at 150 in./mi (2,367.44 mm/km) and 220 in./mi (3,472.24 mm/km), respectively.

This paper focuses on studying the damped properties of damped free vibration for single-degree-of-freedom system by using the Noether symmetries. Based on the Noether theorem, the damping coefficient and amplitude of the damped free vibration system were derived. It is shown that this method of symmetries is useful in studying damped vibration of dynamics of structure. An example is presented to illustrate these results.

This paper proposes a new dynamic participation factor (DPF) for analysis and design of structures supporting rotational machines, especially large turbine generators. The new DPF takes into account the distribution patterns of the machine unbalanced forces and addresses the phase lags among the forces at different bearings and between the different force components. An example of a real turbine-generator foundation is presented and the new and traditional DPFs are compared along with examination of the vibration modes. The results show that the new DPF can clearly identify the local vibration modes that cause severe resonance. Using the traditional DPF could cause engineers to ignore these modes and, consequently, result in unsafe design. The common misconceptions of dominant fundamental modes and low tuning are clarified. Harmonic analyses (frequency sweeps) are also performed and the results are compared with the results of the new DPF analyses. The new DPF analysis has clear advantages over the harmonic analysis in that it provides a complete picture of the dynamic behavior of the whole structure and does not need the engineer to anticipate the local vibration points. The new DPF analysis can also be used to guide the selection of locations for vibration amplitude check and provides an alternative method to consider the different phasing of bearing loadings, which produces responses to real loading cases.

Powerful computers on each designer’s desk, improvements in simulation technique, and advances in the reliability assessment theory make it possible to consider a transition from prescriptive concepts, such as partial factor design (PFD), to fully probabilistic concepts applicable in design practice, such as the feasible simulation-based reliability assessment (SBRA) method. Using a pilot example, the main differences between the PFD assessment procedure and SBRA procedure are demonstrated and described. Attention is focused on the substance of individual steps starting with the assignment (including a representation of loading, mechanical, and geometrical properties of the structure and characteristics of imperfections) and concluding the comparison with safety limits expressed vis-à-vis PFD by a ratio of demand and capacity (to be less than 1.0) and regarding SBRA by comparing the probability of failure $P_f$ and design (target) probability $P_d$ , i.e., $P_f<P_d$ . The potential, efficiency, and advantages of the proposed SBRA method are elucidated.

Self-supported direct-embedded poles are widely used by the utility industry in the United States to support high-voltage transmission lines. For a typical transmission pole, the lateral loads caused by wind and ice loadings govern the design of the pole and foundation. Recent research findings reveal that the methods used in current practice do not yield consistently reliable pole foundation embedment depths in all soil types and for all possible pole classes, lengths, species, and pole loading scenarios. In order to generate improved design methods for transmission pole foundations, validated methods for analyzing laterally loaded piles have been incorporated into the current study. New reliable methods to design safe and cost-effective transmission pole foundations, incorporating both soil and pole properties, are proposed and recommendations are made in rigorous and simplified forms such that they can be easily adopted for use in the utility industry. This study found that the current methods for determining embedment depths for relatively rigid transmission poles significantly underestimate or overestimate the required embedment depths depending on the pole and soil properties by as much as ±60%. A field case study is presented, where direct-embedded round wood transmission poles fell over due to foundation failure, and the results of this case study are compared to the methods presented in this paper. The proposed methods are also compared with PLS-Caisson software predictions, and it is determined that the methods proposed in this paper are relatively easy to use and generate accurate and reliable results.

In thermal power plants, steam generating equipment (high-pressure boilers) and its auxiliaries are in great need of usage of steel structures. The supporting system for the equipment and auxiliaries should be designed carefully after proper analysis by considering the various loads acting over it. The supporting structure should be stable, safe for the imposed loads and reliable for the equipment to function effectively. Generally, the structure is designed without considering the effect due to differential settlement. This settlement is caused due to unequal loads, heterogeneity in soil characteristics, fluctuations in ground water table etc. The present study evaluates the effect of interplanar differential settlement of isolated reinforced concrete footings on vertical loading for a boiler supporting structure. This work is in further continuation of the earlier study carried out for the same boiler supporting structure to determine the effect of intraplanar differential settlement on vertical loading by the writers presented in the subsequent sections of this paper. STAAD-III software is used for the modeling and analysis of the structure to determine the vertical load acting on each footing. A total of 430 combination trials are performed and the load factors for the various magnitudes of settlement are established. The percentage increase in vertical load is observed as 17, 20, 24, 28, and 44% for differential settlement of 10, 20, 30, 40, and 50 mm, respectively. Comparisons of increase in vertical load for each column are made between the intraplanar and interplanar differential settlement analyses. It is observed that similar columns are found to be affected for the maximum percentage increase in vertical load and the variation is marginal except for 50 mm differential settlement.

The stiffness of eccentrically braced frames (EBFs) is difficult to calculate by hand because they are indeterminate and have significant flexural, shear, and axial deformations in various members. EBF stiffness is important because it is used to compute story drifts and link rotations which have prescribed limits. This note presents an equation for the stiffness of an EBF story in terms of the design story shear, frame geometry, and beam depth. The equation is independent of specific member sizes, making it useful for determining appropriate geometry in early design. The equation is developed theoretically and validated with data from code compliant EBFs. One application of the equation is the direct calculation of the minimum beam depth required to ensure a link will satisfy inelastic rotation limits.