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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. [ABSTRACT FROM AUTHOR]

A high-density polyethylene (HDPE) geogrid soil-reinforced dry-cast concrete block retaining wall 6.3-m high was designed using the K-stiffness method as part of a highway-widening project southeast of Seattle, Washington. The amount of reinforcement needed for the original wall design using the K-stiffness method was approximately 50% of that required using the AASHTO simplified method. This paper describes the construction, instrumentation program, and interpretation of the measurements. Geogrid strains were measured using strain gauges and extensometers attached to reinforcement layers. An extensive materials testing program was conducted to characterize the backfill soil properties and geogrid stiffness properties and to calibrate strain gauge readings. The reinforcement loads deduced from the measured strains are compared with Class A, B, and C1 predictions using the AASHTO simplified and K-stiffness methods. These comparisons demonstrate that the simplified method significantly overestimated reinforcement loads, whereas the K-stiffness method provided estimates that were consistent with the measured results. This paper describes lessons learned, the influence of construction activities on wall performance, and the limitations of both methods in estimating connections loads. [ABSTRACT FROM AUTHOR]

Centrifuge models of soft-clay deposits were shaken with suites of earthquake ground motions to study site response over a wide strain range. The models were constructed in an innovative hinged-plate container to effectively reproduce one-dimensional ground-response boundary conditions. Dense sensor arrays facilitate back-calculation of modulus-reduction and damping values that show modest misfits from empirical models. Low-amplitude base motions produced nearly elastic response in which ground motions were amplified through the soil column, and the fundamental site period was approximately 1.0 s. High-intensity base motions produced shear strains higher than 10%, mobilizing shear failure in clay at stresses larger than the undrained monotonic shear strength. The authors attribute these high mobilized stresses to rate effects, which should be considered in strength-parameter selection for nonlinear analysis. This nonlinear response deamplified short-period spectral accelerations and lengthened the site period to 3.0 s. The nonlinearity in spectral amplification is parameterized in a form used for site terms in ground-motion prediction equations to provide empirical constraint unavailable from ground-motion databases. [ABSTRACT FROM AUTHOR]

Accurately predicting peak penetration resistance qpeak during spudcan installation into sand overlying clay is crucial to an offshore mobile jack-up industry still suffering regular punch-through failures. This paper describes a series of spudcan penetration tests performed on medium-loose sand overlying clay and compares the response to existing centrifuge data from tests performed on dense sand overlying clay. Together these data demonstrate that punch-through is a potential problem for both dense and loose sand overlying clay soil stratigraphies. Using this experimental database, a failure-stress-dependent model has been modified to account for the embedment depth, and the depth of occurrence of qpeak is shown to be a function of the sand thickness Hs. The model then was recalibrated, taking these findings into account, for a larger range of material properties and ratios of sand thickness to spudcan diameter (Hs=D). Finally, the performance of the modified and recalibrated model is verified by comparing its predictions with those calculated using current guidelines. The comparisons show that the modified model yields more accurate predictions of qpeak over the range of Hs=D ratios of practical interest, which when used in practice will potentially mitigate the risk of unexpected punch-through on sand overlying clay stratigraphies. [ABSTRACT FROM AUTHOR]

Interpretation of experimental and field cone penetration test (CPT) data from across a broad range of stress conditions requires defining the dependence of the measurements on overburden stress and other influencing factors. This paper examines three possible methods for overburden normalization of CPT tip resistance in sand at the same state parameter or same relative state parameter. The three methods for determining state-based normalized tip resistance at a reference overburden stress of 101.3 kPa (1 atm) are evaluated against calibration chamber test data for four well-studied clean sands. The CPT data from the calibration chamber tests are corrected for chamber boundary effects using two different methods to illustrate the effect this step has on derived relationships. The CPT data are further normalized to a common lateral earth pressure coefficient to illustrate the effect of this step. The three methods for state-based overburden normalization were evaluated for bias and dispersion against the calibration chamber data, including their dependence on the applied chamber correction relationship. The dependence of state-based overburden normalized tip resistances on the crushing behavior of the clean sand was evaluated by examination of one-dimensional limiting compression curves for these four sands. Finally, correlations for estimating the state parameter or relative state parameter from the state-based overburden normalized tip resistance were developed and evaluated based on the examined data. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate the effectiveness of an alternative technique for strengthening masonry columns, based on the use of steel cords. Although fiber-reinforced polymer (FRP) strips or jackets are successfully used as strengthening elements for this kind of application, such a strengthening method represents a new opportunity to restore ambit, with considerable development in unreinforced masonry wrapping. Thus, to assess the potential of steel cord wrapping, this paper presents the results of an experimental program consisting of 48 solid-brick specimens subjected to uniaxial compression load. Different cross-section geometry (octagonal, square, and rectangular) and different amounts and different schemes for confining reinforcement were investigated. The primary experimental outcomes are presented and discussed in the paper considering the mechanical behavior of specimens and the axial stress-axial strain relationships. Test results have shown that the investigated confining systems are able to provide significant gains, both in the compressive strength and in the deformation capacity of masonry columns. [ABSTRACT FROM AUTHOR]

Results of an extensive series of repeated load triaxial tests performed on three major recycled construction and demolition (C&D) materials at various moisture contents and stress levels were analysed to ascertain their performance in pavement subbases. The development of the resulting permanent deformation that accumulates with the repeated loading and the determination of resilient modulus by two phases of the test are described. The experimental study shows that the C&D materials perform satisfactorily at a moisture content of about 70% of their optimum moisture contents. Furthermore, the C&D materials also satisfy the two-parameter and three-parameter models. The results of this study indicate that, at a density ratio of 98% compared to maximum dry density obtained in the modified proctor test and with moisture contents in the range of 65-90% of the optimum moisture content, most of the recycled C&D materials produce comparatively smaller permanent strain and greater resilient modulus than natural commonly used granular subbase materials in pavement subbase applications. [ABSTRACT FROM AUTHOR]

Given the schedule pressure of lime-stabilized soil construction, many agencies specify the use of elevated temperature (e.g., 41°C), shorter duration (e.g., 5-7 days) accelerated specimen curing for unconfined compressive strength () testing and acceptance as a proxy for of specimens normally cured under 28-day 23°C conditions. Moreover, lime and highway transportation industry associations prescribe a unique accelerated curing regime for all lime-stabilized soils (7-day, 41°C). This paper presents the results from a laboratory investigation of stress-strain-strength development of four lime-stabilized soils under 2-8 day 41°C accelerated curing and the 0-28 day 23°C normal curing regime. Specimens cured at 41°C reached values equivalent to 28-day 23°C after 1.8-5.9 days. Accordingly, 7-day 41°C curing overestimates 28-day normal cure by 13-260%. When combined with a detailed analysis of data available in the literature, the results illustrate that the prescription of a unique equivalent accelerated curing regime is oversimplified and can lead to significant overestimation of design . [ABSTRACT FROM AUTHOR]

In this paper, the importance of displacement history and its effects on performance limit states, the relationship between strain and displacement, and the spread of plasticity in RC structures is explored. An experimental study is underway to assess the performance of 30 circular, well-confined, bridge columns with varying lateral displacement history, transverse reinforcement detailing, axial load, aspect ratio, and longitudinal steel content. Eight of these columns, with similar geometry and detailing, were subjected to various unidirectional displacement histories including standardized laboratory reversed cyclic loading and re-creations of the displacement responses obtained from a nonlinear time-history analysis of multiple earthquakes with distinct characteristics. Longitudinal reinforcing bars were instrumented to obtain strain hysteresis, vertical strain profiles, cross section curvatures, curvature distributions, and fixed-end rotations attributable to strain penetration. Results have shown that the limit state of reinforcement bar buckling was influenced by load history, but the relationship between strain and displacement along the envelope curve was not. The main impact of load history on bar buckling is its influence on accumulated strains within the longitudinal reinforcement and transverse steel. [ABSTRACT FROM AUTHOR]

This paper presents a comparison of two live-load tests performed on a posttensioned, box-girder bridge. The initial live-load test was performed more than 20 years before the most recent test. Strain gauges were placed at the same location for both tests. In each case, the bridge was subjected to nearly identical loads so that changes in strain could be correlated as a heavy truck drove across the instrumented bridge. A comparison of the bridge behavior based on the two load tests is presented. The changes in recorded strain were also used to validate a detailed finite-element (FE) model using primarily shell elements. From this calibrated FE model, the live-load distribution factors for moment were obtained. These factors were used to calculate both the inventory and operating rating factors of the bridge. These values were compared with those calculated in accordance to the AASHTO LRFD specifications for distribution factors. It was found that the rating factors could be increased by 26% because of the partial fixity caused by the integral abutments. [ABSTRACT FROM AUTHOR]

Experimental research on imposed deformation is generally conducted on small-scale laboratory experiments. The attractiveness of field research lies in the possibility to compare results obtained from full-scale structures to theoretical predictions. Unfortunately, measurements obtained from real structures are rarely described in literature. The structural response of integral edifices depends significantly on stiffness changes and constraints. The New Airport Terminal Barajas in Madrid, Spain provides investigators with large integral modules, partially post-tensioned concrete frames, cast monolithically over three floor levels with an overall length of approximately 80 m. The field campaign described in this article explains the instrumentation of one of these frames, focusing on the influence of imposed deformations such as creep, shrinkage, and temperature. The applied monitoring equipment included embedded strain gauges, thermocouples, hand-held mechanical strain gauge measurements, and simple displacement measurements. Data were collected throughout construction and during two years of service. A complete data range of five years is presented and analyzed. Using a simple approach, the results are compared to predict the long-term shortening of this concrete structure. Both analytical and experimental results are discussed. [ABSTRACT FROM AUTHOR]

By analyzing the field data from nine metro-station pits with aspect ratios (AR) of pit length to width of 6.6-19.4 in Shanghai soft clay, this paper investigates the potential corner effects (i.e., the retaining walls near pit corners have stronger capabilities to resist deformation than those distant away as a product of spatial arching effects across the pit corners) of long and narrow multipropped metro station excavations. Contrary to the two-dimensional (2D) plane-strain assumption widely adopted in practice for analysis of a metro station excavation (i.e., deformations of the pit in which the displacements of all points along the longitudinal sides are assumed to be parallel to a given plane in the transverse direction and the values of these displacements do not depend on the distance perpendicular to the plane), seven out of the nine metro station pits exhibited apparent corner effects and only two showed plane-strain conditions. Because of the stiffening effects from the pit corners, the minimum wall deflections occurred near the pit corners and the maximum occurred near the middle span of the pits. The development of the maximum wall deflections along the longitudinal sides of the pits, which were normalized by the final excavation depths, can be bounded by two liner curves. Because of their narrow widths, the observed corner effects of the metro stations were less pronounced than that of a rectangular excavation with an AR of about 2.0. Distinctly different from the findings in literature for regular rectangular excavations with AR of 1.0-2.0, the variation of either the pit length-to-depth ratio or the pit length-to-width ratio hardly affected the corner effects of metro station pits. The derived graphical solutions accounting for the influence of pit lengths on corner stiffening effects can be used as references for future design and construction of a long and narrow multipropped pit in soft clays. The monitoring data regarding the adjacent building settlements demonstrate that the mobilized corner stiffening effects during excavation were helpful in constraining the ground deformation and protecting the structures or facilities in the proximity. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the aggregate contact behavior in asphalt mixture. As a three-phase material composed of aggregates, asphalt binder, and air voids, asphalt mixture is considered as a viscoelastic material at a low stress level. The behavior of the mixture depends largely on the interaction among different components. A contact model between two aggregates is very important for understanding the deformation mechanism of the mixture. In this study, a contact model between two aggregates was reviewed in details. A closed-form time-dependent relationship between the contact forces and the relative particle/binder movements was derived. An experimental test was designed to evaluate the model which contains two elastic particles bonded by a thin layer of asphalt binder. The displacement and resistant force of the aggregate-binder system under uniaxial compression loading were documented using a cabinet X-ray tomography system. The effectiveness of the model was evaluated by comparing the experimental results with the theoretical model predictions. It was found that the model performs better when the thickness of binder is thinner. Polynomial regression equations are more suitable to fit the model-predicted results with experimental results. Selection of the model parameters is also critical to the performance of the model. The effect of the binder film thickness on the aggregate-aggregate contact was also discussed with different binder layer thicknesses. It was found that the stiffness of the aggregate-binder-aggregate system increases as the bonding layer gets thinner, which indicates that optimum asphalt content is very important to the mix design of asphalt concrete. [ABSTRACT FROM AUTHOR]

Shear deformation of -Sn along five different lattice orientations is studied at the atomic level. Simulated models are perfect -Sn lattice without defects. To study the atomic behavior and constitutive relationship of -Sn in shear, the -Sn models are simulated by a molecular dynamics simulation package, LAMMPS, and the shear stress is computed by using virial stress. A modified embedded-atom method is employed for the -Sn potential. The constant shear strain rate, 17.5 (%/ns), is applied. Simulation is conducted by using a canonical ensemble. To investigate thermal effects, the models are simulated at three different temperatures, 27, 127, and 227°C, and the results were compared with experimental data. [ABSTRACT FROM AUTHOR]