Optimum Concrete Mixture Proportion Based on a Database Considering Regional Characteristics

This paper presents an enhanced design methodology for optimal mixture proportion of concrete composition with respect to accuracy in the case of using prediction models based on a limited database. In proposed methodology, the search space is constrained as the domain defined by a limited database instead of constructing the database covering the region represented by the possible ranges of all variables in the input space. A model for defining the search space which is expressed by the effective region in this paper and evaluating whether a mix proportion is effective is added to the optimization process, yielding highly reliable results. To demonstrate the proposed methodology, a genetic algorithm, an artificial neural network, and a convex hull were adopted as an optimum technique, a prediction model for material properties, and an evaluation model for the effective region, respectively. And then, it was applied to an optimization problem wherein the minimum cost should be obtained under a given strength requirement. Experimental test results show that the mix proportion obtained from the proposed methodology considering the regional characteristics of the database is found to be more accurate and feasible than that obtained from a general optimum technique that does not consider this aspect.     

Generation and application of type-specific anti-heparan sulfate antibodies using phage display technology. Further evidence for heparan sulfate heterogeneity in the kidney

Detailed analysis of various heparan sulfate (HS) species is seriously hampered by a lack of appropriate tools, such as antibodies. We adopted phage display technology to generate anti-HS antibodies. A "single pot" semisynthetic human antibody phage display library was subjected to four rounds of selection on HS from bovine kidney using panning methodology. Three different phage clones expressing anti-HS single chain variable fragment antibodies (HS4C3, HS4D10, and HS3G8) were isolated, with an amino acid sequence of the complementarity-determining region 3 of GRRLKD (VH3 gene, DP-38), SLRMNGCGAHQ (VH3 gene, DP-42), and YYHYKVN (VH1 gene, DP-8), respectively. The antibodies react with HS and heparin, but not with DNA or other glycosaminoglycans. Kd values for HS are about 0.1 microM. The three antibodies react differently toward various HS preparations and show different staining patterns on rat kidney sections, indicating recognition of different HS molecules. This also holds for two described mouse anti-HS IgMs (JM403 and 10E4; both generated by conventional hybridoma technique) and indicates the presence of at least 5 different HS species in the kidney. O- and N-sulfation are important for binding of HS to HS4C3 and HS3G8. The three single chain antibodies, but not JM403, block a basic fibroblast growth factor binding site of HS. It is concluded that phage display technology presents a powerful technique to generate antibodies specific for HS epitopes. This is the first time this technique has been successfully applied to obtain directly antibodies to (poly)saccharides.     

Live Load Tests of the San Antonio “Y”

This paper presents the results of static live load tests performed on several spans of the San Antonio “Y” Project, Phase IIC, prior to its opening to traffic. The San Antonio “Y” Project is an urban viaduct comprising primarily precast segmental box girders erected using span-by-span methods and utilizing a mix of internal and external posttensioning tendons. As part of a comprehensive field investigation, four spans of the project were instrumented to measure overall span deflections, strains in external posttensioning tendons, and concrete surface strains. The four instrumented spans included one end span and the center span of a three-span continuous unit, one span of a two-span ramp unit that was transversely posttensioned to the adjacent main line unit, and one span of a two-span unit connected only with a continuous top slab over the center support (so called “poor boy” continuity). The spans were loaded using combinations of heavily loaded 7-yd short-bed dump trucks positioned to simulate AASHTO MS18 (HS20-44) truckloads. Measurements of span deflections, external tendon strains, and limited concrete surface strains are reported and compared with analytical predictions. Overall, the bridge spans behaved very predictably under static live load conditions.     

轻骨料混凝土在筒仓工程中的应用

论述了筒仓工程中以部分轻骨料混凝土代替普通混凝土的应用研究,阐述了轻骨料混凝土在工程应用中的配合比设计方法,并对轻骨料混凝土在筒仓工程中的经济效益提出了一些建议,为工程技术人员和轻骨料混凝土研究人员提供了一些数据参考.     

矿渣-粉煤灰基高性能混凝土专用胶凝材料

通过优化配比组分、粒级设计和使用外加剂,制备出一种高掺量矿渣、粉煤灰且使用水泥熟料较少的矿渣-粉煤灰基高性能混凝土专用胶凝材料.研究了物料粉磨方式、石膏掺量、矿渣与粉煤灰的掺量及比例对复合高性能胶凝材料体系强度的影响,并通过X射线衍射(XRD)和扫描电镜(SEM)微观分析手段观察其微观结构和水化产物,阐明了复合胶凝材料活性与级配协同优化效应.复合胶凝材料胶砂水胶比为0.36时具有较好的流动度,胶砂试块养护28d抗压强度可以达到58.9MPa,抗折强度达到14.2MPa,并具有良好的抗硫酸盐侵蚀性能,配制的混凝土具有良好的抗碳化性能.     

Experimental Study on the Performance of Approach Slabs under Deteriorating Soil Washout Conditions

In the U.S. bridge design practice, an approach slab is commonly provided to facilitate a smooth transition from the highway pavement to the bridge deck. Maintenance of bridge approaches often necessitates the repair or replacement of approach slabs owing to damage from heavy traffic loads, washout of fill materials, and settlement of the approach embankment. Approach slab damage because of embankment settlement is considered a more common problem and has been extensively investigated in the literature. In this paper, performance of the approach slab degraded by void formation underneath the slab is examined by load testing. Full-size approach-slab specimens were tested under increasing magnitude up to four times AASHTO HS20-44 design truck loads. The test matrix included four slab specimens with the following details: (1)?conventional steel reinforcement representative of current California design; (2)?steel reinforcement replaced by a double-layer pultruded fiber-reinforced polymer grating; (3)?steel reinforcement replaced by glass fiber-reinforced polymer rebars; and (4)?incorporation of steel and polyvinyl alcohol fibers in the concrete mix and removal of top longitudinal and transverse steel. Results indicated that the slabs show satisfactory performance under standard HS20-44 design truck load. Tests also revealed that these slabs exhibited similar performance in terms of stiffness, deformation, and crack pattern when fully supported, but registered noticeable difference in performance under deteriorating soil washout conditions. The fiber-reinforced concrete slab in general showed the best crack control and the smallest deflection and end rotation among the four slabs.     

Case Study-Based Challenges of Quality Concrete Finishing for Architecturally Complex Structures

This paper focuses on the procedure utilized in the construction of tilt-up irregular concrete panels that are constructed on-site using concrete slabs and wooden formwork. The case study required high-quality concrete finishing. The erection and installation procedure called for a maximum panel-to-panel joint tolerance of 1.27?cm (0.5?in.), often 90° joints between panels. To meet precision requirements, the casting slabs were leveled and flattened with laser screed technology and smoothed with chemical solutions. To ensure that the final result met expectations, a mock-up model was built using different types of materials and to simulate site constraints. The architectural design is a composition of precast concrete panels like “Lego” pieces assembled similarly to a jigsaw puzzle. The unique construction process required a state-of-the-art analysis to produce the set quality. Quality conditions as set by the owner included creating a smooth concrete surface on all panels while avoiding damages and reducing equipment and material costs. The proposed methodology is described through its implementation on the case study, which is also described in this paper.     

Hybrid Models of Neural Networks and Genetic Algorithms for Predicting Preliminary Cost Estimates

This technical note applies hybrid models of neural networks (NN) and genetic algorithms (GA) to cost estimation of residential buildings to predict preliminary cost estimates. Data used in the study are for residential buildings constructed from 1997 to 2000 in Seoul, Korea. These are used in training each model and evaluating its performance. The models applied were Model I, which determines each parameter of a back-propagation network by a trial-and-error process; Model II, which determines each parameter of a back-propagation network by GAs; and Model III, which trains weights of NNs using genetic algorithms. The research revealed that optimizing each parameter of back-propagation networks using GAs is most effective in estimating the preliminary costs of residential buildings. Therefore, GAs may help estimators overcome the problem of the lack of adequate rules for determining the parameters of NNs.     

Roca Spur Bridge: The Implementation of an Innovative Deicing Technology

The heated deck of Roca Spur Bridge is the first implementation in the world using conductive concrete for deicing. Conductive concrete is a concrete mix containing a certain amount of electrically conductive components in a regular concrete matrix, designed to enable conduction of electricity. Due to its electrical resistance, conductive concrete can generate enough heat to prevent ice formation on a paved surface when connected to a power source.     

Study of Turkish Bridge Standards Involving a Reinforced Concrete Arch Bridge

Turkish bridge design standards were studied with a focus on the live load. Turkish design specifications were compared with American design specifications. Turkish bridge design specifications follow American Association of State Highway and Transportation Officials-Standard Specifications for Highway Bridges (AASHTO-SSHB), with the live load in Turkish standards given in tonnes, whereas in AASHTO-SSHB the live load is in tons. Turkish bridges are currently designed to either HS20 or HS30, the latter being 65% heavier than HS20-44. A reinforced concrete open spandrel arch bridge in Birecik, Turkey was analyzed using a service load approach according to AASHTO-SSHB with a heavy equipment transporter (HET), weighing 104,600?kg, as the live load. Dead load, live load, and impact were considered, and the analysis did not include any modification for possible deterioration, damage, or aging of the bridge. The bridge was not deemed adequate for passage of a HET using these assumptions.     

Role of Learning Algorithm in Neural Network-Based Backcalculation of Flexible Pavements

Nondestructive testing (NDT) methods are widely used for the performance evaluation of flexible pavements. Falling weight deflectometer (FWD), which measures time-domain deflections resulting from applied impulse loads, is the most popular technique among all NDT methods. The evaluation of the FWD data requires the inversion of mechanical pavement properties using a backcalculation tool that includes both a forward pavement response model and an optimization algorithm. Neural networks (NNs) have also emerged as alternative tools that can be employed for pavement backcalculation problems relative to their real-time processing abilities. However, there have been no comprehensive analyses in previous studies that focus on the learning algorithm and the architecture of a NN model, which considerably affect backcalculation results. In this study, 284 different NN models were developed using synthetic training and testing databases obtained by layered elastic theory. Results indicated that both the learning algorithm and network architecture play important roles in the performance of the NN based backcalculation process.     

Micromechanical Modeling of the Viscoelastic Behavior of Asphalt Mixtures Using the Discrete-Element Method

This paper presents a methodology for analyzing the viscoelastic response of asphalt mixtures using the discrete-element method (DEM). Two unmodified (neat) and seven modified binders were mixed with the same aggregate blend in order to prepare the nine hot mix asphalt (HMA) mixtures used in this study. The HMA microstructure was captured using images of vertically cut sections of specimens. The captured grayscale images were processed into black and white images representing the mastic and the aggregate phases, respectively. These microstructure images were used to represent the DEM model geometry. Rheological data for the nine binders were obtained using the dynamic shear rheometer. These data were used to estimate the parameters of the viscoelastic contact models that define the interaction among the mix constituents. The DEM models were subjected to sinusoidal loads similar to those applied in the simple performance test (SPT). The DEM model predictions compared favorably with the SPT measurements. However, the simulation results tended to overpredict the dynamic modulus, E*, for mixtures made with neat binders and underpredict E* for those that consisted of modified binders. The DEM models gave mix phase angles, ?mix, higher than the experimental measurements.     

Corrosion Response of a Decommissioned Deteriorated Bridge Deck

This paper summarizes the results of field tests on the decommissioned Montreal Dickson Bridge, undertaken over a grid of 0.25 by 0.25?m on four randomly selected 5 by 6?m deck patches, and the associated laboratory tests as part of a detailed research program aimed at determining why the bridge deteriorated so rapidly. The basic cause of deterioration was determined to be the lack of quality control (concrete mix composition, placing, compaction, and curing) and the resulting higher permeability of the concrete cover and the associated chloride ion ingress. As a consequence, the resistivity of the concrete was low and reflected in a high steel bar mass loss due to corrosion at several locations on the bridge after a period of only 35 years.     

Assessment of Concrete in Sulfate Soils

An investigation of concrete exposed to sulfate soils is used to illustrate a methodology for the systematic study of the condition of concrete in service. Condition surveys of the site and tests of engineering properties of the concrete were supplemented by examination of concrete cores using the stereomicroscope, the optical microscope, the electron microscope, analysis by wet chemistry, thermal analysis, and X-ray diffraction. Step-by-step progression from large scale (tens of meters) to submicroscopic scales (tens of nanometers) gave continuity to detailed test methods. It also allowed for the selection of specimens appropriately representing the concrete as a whole, and ensured reliable interpretation of the results. In many cases, more than one test method provided the same or similar information. The writers believe the methodology employed will be of value to other investigators.     

Seismic Safety Assessment of Gated Spillways

This paper presents an innovative three-dimensional performance-based earthquake engineering assessment methodology for gated spillways. Several functionality and structural stability limit states are defined. The functionality of the gates is tackled by assessing seismic demand-to-capacity indices along a success path leading to postearthquake gate opening. As an application example, the proposed methodology is applied to an existing gated spillway built in 1927. Finite element incremental dynamic analyses are performed for six sets of spectrum compatible ground motions with return periods ranging from 200?to?10,000?years. Linear transient dynamic analyses are first performed to compute internal force resultants, displacements, and distortions in structural components. For the concrete structures, the forces from the analyses are input in a postprocessor to compute sliding safety factors using a three-dimensional extension of the gravity method accounting for concrete cracking. The assessment of the hoist supporting structure and gates is done using current steel member demand-to-capacity checks. The actual failure mode hierarchy is identified and found unsatisfactory as the concrete structures and steel lifting tower anchors are expected to fail prematurely. Specific performance criteria and related ground motion return periods are proposed (1) to maintain normal gate opening; (2) to maintain the load bearing capacity of the steel towers and bridge; (3) for life safety of personnel; and (4) to avoid an uncontrolled release of the reservoir.     

ECG processing techniques based on neural networks and bidirectional associative memories

Two ECG processing techniques are described for the classification of QRSs, PVCs and normal and ischaemic beats. The techniques use neural network (NN) technology in two ways. The first technique, uses nonlinear ECG mapping preprocessing and subsequently for classification uses a shrinking algorithm based on NNs. This technique is applied to the QRS/PVC problem with good result. The second technique is based on the Bidirectional Associative Memory (BAM) NN and is used to distinguish normal from ischaemic beats. In this technique the ECG beat is treated as a digitized image which is then transformed into a bipolar vector suitable for input in the BAM. The results show that this method, if properly calibrated, can result in a fast and reliable ischaemic beat detection algorithm.     

Bridge Management and Nondestructive Evaluation

The City and County of Denver (CCD) Public Works Department owns, inspects, and maintains 531 bridges in its inventory of which 264 are considered major structures spanning over 6.1?m in length. In this paper, a methodology using the CCD major bridge network for the application of nondestructive evaluation (NDE) methods in bridge inspections is explained. The methodology, called Bridge Evaluation using Nondestructive Testing (BENT) helps systematically integrate NDE methods and conventional bridge management systems by using a Markovian deterioration model. Although the BENT method can be applied to timber, steel, and concrete bridges, in this paper the application of the method will be restricted to concrete bridges. The BENT system is part of a comprehensive geographic information system whereby database queries can be completed using a map interface. The database contains a wide array of information in the CCD infrastructure inventory including bridges, pavements, alleys, and street subsystems.     

Estimating the Acceptability of New Formwork Systems Using Neural Networks

Continual development in construction techniques results in emergence of specialized formwork systems. A new system will have to compete with in-use systems for adoption in a target operation. Thus, it is essential that decision makers anticipate the acceptability of new systems before making decisions to acquire them. Estimating acceptability basically assesses how features of a new system are comparable to that of in-use systems. Therefore, analogy is a focal factor for the acceptability estimating process. Neural networks (NNs) are more suitable to model construction problems requiring analogy-based solutions. A NN-based approach was employed to anticipate the acceptability of new formwork systems. The study collected data from a group of 40 users in Egypt. A set of six performance characteristics that mostly pertain to acceptability estimating were identified. The study used the analytical hierarchy process to produce pairs of a performance characteristics’ vector and the corresponding acceptability value, and utilized the developed pairs to train NNs. Finally, tests on trained NNs using unseen data indicated satisfactory performance.     

Multivalent ligand-receptor binding interactions in the fibroblast growth factor system produce a cooperative growth factor and heparin mechanism for receptor dimerization

The binding interactions for the three primary reactants of the fibroblast growth factor (FGF) system, basic FGF (bFGF), an FGF receptor, FGFR1, and the cofactor heparin/heparan sulfate (HS), were explored by isothermal titrating calorimetry, ultracentrifugation, and molecular modeling. The binding reactions were first dissected into three binary reactions: (1) FGFR1 + bFGF<==>FGFR1/bFGF, K1 = 41 (+/- 12) nM; (2) FGFR1 + HS<==>FGFR1/HS, K2 = 104 (+/- 17) microM; and (3) bFGF + HS<==>bFGF/HS, K3 = 470 (+/- 20) nM, where HS = low MW heparin, approximately 3 kDa. The first, binding of bFGF to FGFR1 in the absence of HS, was found to be a simple binary binding reaction that is enthalpy dominated and characterized by a single equilibrium constant, K1. The conditional reactions of bFGF and FGFR1 in the presence of heparin were then examined under conditions that saturate only the bFGF heparin site (1.5 equiv of HS/bFGF) or saturate the HS binding sites of both bFGF and FGFR1 (1.0 mM HS). Both 3-and 5-kDa low MW heparins increased the affinity for FGFR1 binding to bFGF by approximately 10-fold (Kd = 4.9 +/- 2.0 nM), relative to the reaction with no HS. In addition, HS, at a minimum of 1.5 equiv/bFGF, induced a second FGFR1 molecule to bind to another lower affinity secondary site on bFGF (K4 = 1.9 +/- 0.7 microM) in an entropy-dominated reaction to yield a quaternary complex containing two FGFR1, one bFGF, and at least one HS. Molecular weight estimates by analytical ultracentrifugation of such fully bound complexes were consistent with this proposed composition. To understand these binding reactions in terms of structural components of FGFR1, a three-dimensional model of FGFR1 was constructed using segment match modeling. Electrostatic potential calculations confirmed that an elongated cluster, approximately 15 x 35 A, of nine cationic residues focused positive potential (+2kBT) to the solvent-exposed beta-sheet A, B, E, C' surface of the D(II) domain model, strongly implicating this locus as the HS binding region of FGFR1. Structural models for HS binding to FGFR1, and HS binding to bFGF, were built individually and then assembled to juxtapose adjacent binding sites for receptor and HS on bFGF, against matching proposed growth factor and HS binding sites on FGFR1. The calorimetric binding results and the molecular modeling exercises suggest that bFGF and HS participate in a concerted bridge mechanism for the dimerization of FGFR1 in vitro and presumably for mitogenic signal transduction in vivo.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of sleep deprivation on driving safety in housestaff

Sleep deprivation is known to affect driving safety. Housestaff (HS) are routinely sleep-deprived when on call. We hypothesized that this would affect their driving. We therefore administered questionnaires regarding driving to 70 pediatric HS, who were on call every fourth night, and to 85 faculty members (FAC), who were rarely disturbed at night. HS were questioned about events during their residency, and FAC were questioned about events during the preceding three years. There was an 87% response rate for each group. HS slept 2.7 +/- 0.9 (SD) hours when on call vs 7.2 +/- 0.8 hours when not on call (p < 0.001). 44% of HS had fallen asleep when stopped at a light, vs 12.5% FAC (p < 0.001). 23% of HS had fallen asleep while driving vs. 8% FAC (ns). A total of 49% of HS had fallen asleep at the wheel; 90% of these events occurred post-call. In contrast, only 13% of FAC had fallen asleep at the wheel (p < 0.001). HS had received a total of 25 traffic citations for moving violations vs. 15 for FAC and were involved in 20 motor vehicle accidents vs. 11 for FAC. One traffic citation clearly resulted from HS falling asleep at the wheel vs. none for FAC. We conclude that HS frequently fall asleep when driving post-call. We speculate that current HS work schedules may place some HS at risk for injury to themselves and others. Further study, using prospectively objective measures is indicated.