Composite Precast Prestressed Concrete Bridge Slabs, HR-310, 1991

Precast prestressed concrete panels have been used as subdecks in bridge construction in Iowa and other states. To investigate the performance of these types of composite slabs at locations adjacent to abutment and pier diaphragms in skewed bridges, a research prcject which involved surveys of design agencies and precast producers, field inspections of existing bridges, analytical studies, and experimental testing was conducted. The survey results from the design agencies and panel producers showed that standardization of precast panel construction would be desirable, that additional inspections at the precast plant and at the bridge site would be beneficial, and that some form of economical study should be undertaken to determine actual cost savings associated with composite slab construction. Three bridges in Hardin County, Iowa were inspected to observe general geometric relationships, construction details, and to note the visual condition of the bridges. Hairline cracks beneath several of the prestressing strands in many of the precast panels were observed, and a slight discoloration of the concrete was seen beneath most of the strands. Also, some rust staining was visible at isolated locations on several panels. Based on the findings of these inspections, future inspections are recommended to monitor the condition of these and other bridges constructed with precast panel subdecks. Five full-scale composite slab specimens were constructed in the Structural Engineering Laboratory at Iowa State University. One specimen modeled bridge deck conditions which are not adjacent to abutment or pier diaphragms, and the other four specimens represented the geometric conditions which occur for skewed diaphragms of 0, 15, 30, and 40 degrees. The specimens were subjected to wheel loads of service and factored level magnitudes at many locations on the slab surface and to concentrated loads which produced failure of the composite slab. The measured slab deflections and bending strains at both service and factored load levels compared reasonably well with the results predicted by simplified Finite element analyses of the specimens. To analytically evaluate the nominal strength for a composite slab specimen, yield-line and punching shear theories were applied. Yield-line limit loads were computed using the crack patterns generated during an ultimate strength test. In most cases, these analyses indicated that the failure mode was not flexural. Since the punching shear limit loads in most instances were close to the failure loads, and since the failure surfaces immediately adjacent to the wheel load footprint appeared to be a truncated prism shape, the probable failure mode for all of the specimens was punching shear. The development lengths for the prestressing strands in the rectangular and trapezoidal shaped panels was qualitatively investigated by monitoring strand slippage at the ends of selected prestressing strands. The initial strand transfer length was established experimentally by monitoring concrete strains during strand detensioning, and this length was verified analytically by a finite element analysis. Even though the computed strand embedment lengths in the panels were not sufficient to fully develop the ultimate strand stress, sufficient stab strength existed. Composite behavior for the slab specimens was evaluated by monitoring slippage between a panel and the topping slab and by computation of the difference in the flexural strains between the top of the precast panel and the underside of the topping slab at various locations. Prior to the failure of a composite slab specimen, a localized loss of composite behavior was detected. The static load strength performance of the composite slab specimens significantly exceeded the design load requirements. Even with skew angles of up to 40 degrees, the nominal strength of the slabs did not appear to be affected when the ultimate strength test load was positioned on the portion of each slab containing the trapezoidal-shaped panel. At service and factored level loads, the joint between precast panels did not appear to influence the load distribution along the length of the specimens. Based on the static load strength of the composite slab specimens, the continued use of precast panels as subdecks in bridge deck construction is recommended.

Lateral Load Resistance of Diaphragms in Prestressed Concrete Girder Bridges, HR-319, 1991

Each year several prestressed concrete girder bridges in Iowa and other states are struck and damaged by vehicles with loads too high to pass under the bridge. Whether or not intermediate diaphragms play a significant role in reducing the effect of these unusual loading conditions has often been a topic of discussion. A study of the effects of the type and location of intermediate diaphragms in prestressed concrete girder bridges when the bridge girder flanges were subjected to various levels of vertical and horizontal loading was undertaken. The purpose of the research was to determine whether steel diaphragms of any conventional configuration can provide adequate protection to minimize the damage to prestressed concrete girders caused by lateral loads, similar to the protection provided by the reinforced concrete intermediate diaphragms presently being used by the Iowa Department of Transportation. The research program conducted and described in this report included the following: A comprehensive literature search and survey questionnaire were undertaken to define the state-of-the-art in the use of intermediate diaphragms in prestressed concrete girder bridges. A full scale, simple span, restressed concrete girder bridge model, containing three beams was constructed and tested with several types of intermediate diaphragms located at the one-third points of the span or at the mid-span. Analytical studies involving a three-dimensional finite element analysis model were used to provide additional information on the behavior of the experimental bridge. The performance of the bridge with no intermediate diaphragms was quite different than that with intermediate diaphragms in place. All intermediate diaphragms tested had some effect in distributing the loads to the slab and other girders, although some diaphragm types performed better than others. The research conducted has indicated that the replacement of the reinforced concrete intermediate diaphragms currently being used in Iowa with structural steel diaphragms may be possible.

Manual for Evaluation, Rehabilitation and Strengthening of Low Volume Bridges, HR-323, 1993

This report contains an evaluation and design manual for strengthening and replacing low volume steel stringer and timber stringer bridges. An advisory panel consisting of county and municipal engineers provided direction for the development of the manual. NBI bridge data, along with results from questionnaires sent to county and municipal engineers were used to formulate the manual. Types of structures shown to have the greatest need for cost-effective strengthening methods are steel stringer and timber stringer bridges. Procedures for strengthening these two types of structures have been developed. Various types of replacement bridges have also been included so that the most cost effective solution for a deficient bridge may be obtained. The key results of this study is an extensive compilation, which can be used by county engineers, of the most effective techniques for strengthening deficient existing bridges. The replacement bridge types included have been used in numerous low volume applications in surrounding states, as well as in Iowa. An economic analysis for determining the cost-effectiveness of the various strengthening methods and replacement bridges is also an important part of the manual. Microcomputer spreadsheet software for several of the strengthening methods, types of replacement bridges and for the economic analysis has been developed, documented and presented in the manual. So the manual, Chp. 3 of the final report, can be easily located, blue divider pages have been inserted to delineate the manual from the rest of the report.

Development of Self-Cleaning Box Culvert Design – Phase II, TR-619, 2013

Culverts are common means to convey flow through the roadway system for small streams. In general, larger flows and road embankment heights entail the use of multibarrel culverts (a.k.a. multi-box) culverts. Box culverts are generally designed to handle events with a 50-year return period, and therefore convey considerably lower flows much of the time. While there are no issues with conveying high flows, many multi-box culverts in Iowa pose a significant problem related to sedimentation. The highly erosive Iowa soils can easily lead to the situation that some of the barrels can silt-in early after their construction, becoming partially filled with sediment in few years. Silting can reduce considerably the capacity of the culvert to handle larger flow events. Phase I of this Iowa Highway Research Board project (TR-545) led to an innovative solution for preventing sedimentation. The solution was comprehensively investigated through laboratory experiments and numerical modeling aimed at screening design alternatives and testing their hydraulic and sediment conveyance performance. Following this study phase, the Technical Advisory Committee suggested to implement the recommended sediment mitigation design to a field site. The site selected for implementation was a 3-box culvert crossing Willow Creek on IA Hwy 1W in Iowa City. The culvert was constructed in 1981 and the first cleanup was needed in 2000. Phase II of the TR 545 entailed the monitoring of the site with and without the selfcleaning sedimentation structure in place (similarly with the study conducted in laboratory). The first monitoring stage (Sept 2010 to December 2012) was aimed at providing a baseline for the operation of the as-designed culvert. In order to support Phase II research, a cleanup of the IA Hwy 1W culvert was conducted in September 2011. Subsequently, a monitoring program was initiated to document the sedimentation produced by individual and multiple storms propagating through the culvert. The first two years of monitoring showed inception of the sedimentation in the first spring following the cleanup. Sedimentation continued to increase throughout the monitoring program following the depositional patterns observed in the laboratory tests and those documented in the pre-cleaning surveys. The second part of Phase II of the study was aimed at monitoring the constructed self-cleaning structure. Since its construction in December 2012, the culvert site was continuously monitored through systematic observations. The evidence garnered in this phase of the study demonstrates the good performance of the self-cleaning structure in mitigating the sediment deposition at culverts. Besides their beneficial role in sediment mitigation, the designed self-cleaning structures maintain a clean and clear area upstream the culvert, keep a healthy flow through the central barrel offering hydraulic and aquatic habitat similar with that in the undisturbed stream reaches upstream and downstream the culvert. It can be concluded that the proposed self-cleaning structural solution “streamlines” the area upstream the culvert in a way that secures the safety of the culvert structure at high flows while producing much less disturbance in the stream behavior compared with the current constructive approaches.

Pile Design and Tests for Integral Abutment Bridges, HR-273, 1987

Expansion joints increase both the initial cost and the maintenance cost of bridges. Integral abutment bridges provide an attractive design alternative because expansion joints are eliminated from the bridge itself. However, the piles in these bridges are subjected to horizontal movement as the bridge expands and contracts during temperature changes. The objective of this research was to develop a method of designing piles for these conditions. Separate field tests simulating a pile and a bridge girder were conducted for three loading cases: (1) vertical load only, (2) horizontal displacement of pile head only, and (3) combined horizontal displacement of pile head with subsequent vertical load. Both tests (1) and (3) reached the same ultimate vertical load, that is, the horizontal displacement had no effect on the vertical load capacity. Several model tests were conducted in sand with a scale factor of about 1:10. Experimental results from both the field and model tests were used to develop the vertical and horizontal load-displacement properties of the soil. These properties were input into the finite element computer program Integral Abutment Bridge Two-Dimensional (IAB2D), which was developed under a previous research contract. Experimental and analytical results compared well for the test cases. Two alternative design methods, both based upon the American Association of State Highway and Transportation Officials (AASHTO) Specification, were developed. Alternative One is quite conservative relative to IAB2D results and does not permit plastic redistribution of forces. Alternative Two is also conservative when compared to IAB2D, but plastic redistribution is permitted. To use Alternative Two, the pile cross section must have sufficient inelastic rotation capacity before local buckling occurs. A design example for a friction pile and an end-bearing pile illustrates both alternatives.

HIV testing in Switzerland.

OBJECTIVES: To obtain information about the prevalence of, reasons for, and adequacy of HIV testing in the general population in Switzerland in 1992. DESIGN: Telephone survey (n = 2800). RESULTS: Some 47% of the sample underwent one HIV test performed through blood donation (24%), voluntary testing (17%) or both (6%). Of the sample, 46% considered themselves well or very well informed about the HIV test. Patients reported unsystematic pre-test screening by doctors for the main HIV risks. People having been in situations of potential exposure to risk were more likely to have had the test than others. Overall, 85% of those HIV-tested had a relevant, generally risk-related reason for having it performed. CONCLUSIONS: HIV testing is widespread in Switzerland. Testing is mostly performed for relevant reasons. Pre-test counselling is poor and an opportunity for prevention is thus lost.

Looking for Validity or Testing It? The Perils of Stepwise Regression, Extreme-Scores Analysis, Heteroscedasticity, and Measurement Error

When researchers introduce a new test they have to demonstrate that it is valid, using unbiased designs and suitable statistical procedures. In this article we use Monte Carlo analyses to highlight how incorrect statistical procedures (i.e., stepwise regression, extreme scores analyses) or ignoring regression assumptions (e.g., heteroscedasticity) contribute to wrong validity estimates. Beyond these demonstrations, and as an example, we re-examined the results reported by Warwick, Nettelbeck, and Ward (2010) concerning the validity of the Ability Emotional Intelligence Measure (AEIM). Warwick et al. used the wrong statistical procedures to conclude that the AEIM was incrementally valid beyond intelligence and personality traits in predicting various outcomes. In our re-analysis, we found that the reliability-corrected multiple correlation of their measures with personality and intelligence was up to .69. Using robust statistical procedures and appropriate controls, we also found that the AEIM did not predict incremental variance in GPA, stress, loneliness, or well-being, demonstrating the importance for testing validity instead of looking for it.

An overall statistic for testing symmetry in social interactions

The present work focuses the attention on the skew-symmetry index as a measure of social reciprocity. This index is based on the correspondence between the amount of behaviour that each individual addresses to its partners and what it receives from them in return. Although the skew-symmetry index enables researchers to describe social groups, statistical inferential tests are required. The main aim of the present study is to propose an overall statistical technique for testing symmetry in experimental conditions, calculating the skew-symmetry statistic (Φ) at group level. Sampling distributions for the skew- symmetry statistic have been estimated by means of a Monte Carlo simulation in order to allow researchers to make statistical decisions. Furthermore, this study will allow researchers to choose the optimal experimental conditions for carrying out their research, as the power of the statistical test has been estimated. This statistical test could be used in experimental social psychology studies in which researchers may control the group size and the number of interactions within dyads.

High Molecular Weight Methacrylate Sealing of a Bridge Deck, HR-2031, 1988

The Iowa Department of Transportation used a high molecular weight methacrylate (HMWM) resin to seal a 3,340 ft. x 64 ft. bridge deck in October 1986. The sealing was necessary to prevent deicing salt brine from entering a substantial number of transverse cracks that coincided with the epoxy coated top steel and unprotected bottom steel. HMWM resin is a three component product composed of a monomer, a cumene hydroperoxide initiator and a cobalt naphthenate promoter. The HMWM was applied with a dual spray bar system and flat-fan nozzles. Initiated monomer delivered through one spray bar was mixed in the air with promoted monomer from the other spray bar. The application rate averaged 0.956 gallons per 100 square feet for the tined textured driving lanes. Dry sand was broadcast on the surface at an average coverage of 0.58 lbs. per square yard to maintain friction. Coring showed that the HMWM resin penetrated the cracks more than two inches deep. Testing of the treated deck yielded Friction Numbers averaging 33 with a treaded tire compared to 36 prior to treatment. An inspection soon after treatment found five leaky cracks in one of the 15 spans. One inspection during a steady rain showed no leakage, but leakage from numerous cracks occurred during a subsequent rain. A second HMWM application was made on two spans. Leakage through the double application occurred during a rain. Neither the single or double application were successful in preventing leakage through the cracks.

Laboratory Testing of SHRP SPS-2 P.C.C. Mixes, MLR-94-5, 1995

This research evaluated the concrete strength of two mixes which were used in the Polk County project NHS-500-1(3)--10-77 and were developed to meet a contract requirement of 900 psi third-point 28-day flexural strength. Two concrete mixes, the Proposed Mix and the Enhanced Mix, were tested for strength. Based on the experimental results, it was found that the addition of 50 lb of cementitious materials did not significantly increase concrete strength. The requirement of 900 psi 28-day third-point flexural strength (MOR-TPL) was not achieved by this amount of addition of cementitious materials.

Lag-one autocorrelation in short series: Estimation and hypothesis testing

In the first part of the study, nine estimators of the first-order autoregressive parameter are reviewed and a new estimator is proposed. The relationships and discrepancies between the estimators are discussed in order to achieve a clear differentiation. In the second part of the study, the precision in the estimation of autocorrelation is studied. The performance of the ten lag-one autocorrelation estimators is compared in terms of Mean Square Error (combining bias and variance) using data series generated by Monte Carlo simulation. The results show that there is not a single optimal estimator for all conditions, suggesting that the estimator ought to be chosen according to sample size and to the information available of the possible direction of the serial dependence. Additionally, the probability of labelling an actually existing autocorrelation as statistically significant is explored using Monte Carlo sampling. The power estimates obtained are quite similar among the tests associated with the different estimators. These estimates evidence the small probability of detecting autocorrelation in series with less than 20 measurement times.

Metric Short Course for the Office of Bridges and Structures, HR-378, 1995

This metric short course was developed in response to a request from the Office of Bridges and Structures to assist in the training of engineers in the use of metric units of measure which will be required in all highway designs and construction after September 30, 1996 (CFR Presidential Executive Order No. 12770). The course notes which are contained in this report, were developed for a half-day course. The course contains a brief review of metrication in the U.S., metric units, prefixes, symbols, basic conversions, etc. The unique part of the course is that it presents several typical bridge calculations (such as capacity of reinforced concrete compression members, strength of pile caps, etc.) worked two ways: inch-pound units throughout with end conversion to metric and initial hard conversion to metric with metric units throughout. Comparisons of partial results and final results (obtained by working the problems the two ways) are made for each of the example problems.

Design Manual for Strengthening of Continuous-Span Composite Bridges, HR-333, 1993

The need for upgrading a large number of understrength bridges in the United States has been well documented in the literature. This manual presents two methods for strengthening continuous-span composite bridges: post-tensioning of the positive moment regions of the bridge stringers and the addition of superimposed trusses at the piers. The use of these two systems is an efficient method of reducing flexural overstresses in undercapacity bridges. Before strengthening a given bridge however, other deficiencies (inadequate shear connection, fatigue problems, extensive corrosion) should be addressed. Since continuous-span composite bridges are indeterminant structures, there is longitudinal and transverse distribution of the strengthening axial forces and moments. This manual basically provides the engineer with a procedure for determining the distribution of strengthening forces and moments throughout the bridge. As a result of the longitudinal and transverse force distribution, the design methodology presented in this manual for continuous-span composite bridges is extremely complex. To simplify the procedure, a spreadsheet has been developed for use by practicing engineers. This design aid greatly simplifies the design of a strengthening system for a given bridge in that it eliminates numerous tedious hand calculations, computes the required force and moment fractions, and performs the necessary iterations for determining the required strengthening forces. The force and moment distribution fraction formulas developed in this manual are primarily for the Iowa DOT V12 and V14 three-span four-stringer bridges. These formulas may be used on other bridges if they are within the limits stated in this manual. Use of the distribution fraction formulas for bridges not within the stated limits is not recommended.