DESIGN AND MECHANICAL PROPERTIES OF FOAMED ASPHALT STABILIZED BASE MATERIAL

Foamed asphalt stabilized base (FASB) combines reclaimed asphalt pavement (RAP) and/or recycled concrete (RC) with a foamed asphalt binder. The pavement structural properties of FASB fall somewhere between conventional graded aggregate base (GAB) and hot mix asphalt (HMA). Therefore, the required thickness of the pavement section can be reduced, resulting in cost savings in addition to recycling benefits. Mix designs were developed for eight different combinations of RAP, RC, and GAB. Details of the mix design procedure and the effects of factors representative of design and field conditions are evaluated. Triaxial test specimens from the weakest and strongest mixtures were tested for dynamic modulus and repeated load permanent deformation resistance, which can be used as inputs to the new AASHTO mechanistic-empirical design procedure. The measured stiffness values were also used to determine an appropriate structural layer coefficient value for use in the AASHTO empirical pavement design method

The Effects of Long-Duration Subduction Earthquakes on Inelastic Behavior of Bridge Pile Foundations Subjected to Liquefaction-Induced Lateral Spreading

Effective-stress nonlinear dynamic analyses (NDA) were performed for a large-diameter reinforced concrete (RC) pile in multi-layered liquefiable sloped ground. The objective was to assess the effects of earthquake duration on the combination of inertia and liquefaction-induced lateral spreading. A parametric study was performed using input motions from subduction and crustal earthquakes covering a wide range of motion durations. The NDA results showed that the pile head displacements increased under liquefied conditions, compared to nonliquefied conditions, due to liquefaction-induced lateral spreading. The NDA results were used to develop a displacement-based equivalent static analysis (ESA) method that combines inertial and lateral spreading loads for estimating elastic and inelastic pile demands

Minimum Required Length for Geotechnical Lateral Stability of RockSocketed Pile Shafts

The original strong-rock (SR) p-y curves for rock-socketed shafts exhibit a brittle response where the post-peak resistance drops to approximately zero. This brittle response could result in a progressive failure of the rock p-y curves which, in turn, results in excessive pile lengths. This paper proposes a modification to the strong-rock (SR) p-y curves where the post-peak residual strength is equal to 20% of the ultimate resistance (0.2*pult). This residual resistance is proposed based on the assumption that the lateral resistance of cracked rock (after the peak point) should not be smaller than the lateral resistance of heavily weathered rock estimated from the weak-rock (WR) and Liang et al. p-y curves. The effectiveness of the modified SR curves is evaluated against the results of a lateral load test. The modified SR curves are compared against back-calculated p-y curves from the lateral load test

Cyclic Porewater Pressure Generation in Intact Silty Soils

The results of cyclic strain-controlled, constant volume direct simple shear (CDSS) tests and field shaking tests have been evaluated for intact, natural, low-plastic silts from six different fine-grained soils with 54%–100% fines content, 47%–83% silt content, and plasticity indices (PI) ranging from nonplastic to 16. These tests constitute a subset of a larger archive of CDSS tests performed on silt deposits from the Pacific Northwest, British Columbia, and Alaska collected and analyzed by the co-authors. The cyclic data are presented in this paper for two objectives: (a) to characterize cyclically-induced excess pore pressure generation in intermediate soils with various soil index properties and stress histories, and (b) to provide calibrated Vucetic and Dobry model parameters for simulating excess pore pressure generation in the silt soils based on the data and trends presented in the first objective. The CDSS test results showed that excess pore pressure ratios decrease with PI over the narrow range of PI evaluated and decrease with overconsolidation ratio. The cyclic threshold shear strain amplitude for pore pressure generation extracted from field shaking tests on silts were within the range proposed in the literature, confirming that the cyclic threshold shear strain amplitude is a fundamental soil property. Calibrated Vucetic and Dobry model parameters for these intermediate, fine-grained silts were significantly different than those reported for sands in the literature and were heavily influenced by the overconsolidation ratio. The calibrated parameters obtained in this study can be used as a benchmark in selecting model parameters for silts

Large-Scale Controlled-Condition Experiment to Evaluate Light Weight Deflectometers for Modulus Determination and Compaction Quality Assurance of Unbound Pavement Materials

Compaction control using lightweight deflectometers (LWD) is currently being evaluated in several states and countries and fully implemented for pavement construction quality assurance (QA) by a few. Broader implementation has been hampered by the lack of a widely recognized standard for interpreting the load and deflection data obtained during construction QA testing. More specifically, reliable and practical procedures are required for relating these measurements to the fundamental material property—modulus—used in pavement design. This study presents a unique set of data and analyses for three different LWDs on a large-scale controlled-condition experiment. Three 4.5x4.5 m2 test pits were designed and constructed at target moisture and density conditions simulating acceptable and unacceptable construction quality. LWD testing was performed on the constructed layers along with static plate loading testing, conventional nuclear gauge moisture-density testing, and non-nuclear gravimetric and volumetric water content measurements. Additional material was collected for routine and exploratory tests in the laboratory. These included grain size distributions, soil classification, moisture-density relations, resilient modulus testing at optimum and field conditions, and an advanced experiment of LWD testing on top of the Proctor compaction mold. This unique large-scale controlled-condition experiment provides an excellent high quality resource of data that can be used by future researchers to find a rigorous, theoretically sound, and straightforward technique for standardizing LWD determination of modulus and construction QA for unbound pavement materials

Trust and Reputation in Multi-Agent Systems

Multi-Agent systems (MAS) are artificial societies populated with distributed autonomous agents that are intelligent and rational. These self-independent agents are capable of independent decision making towards their predefined goals. These goals might be common between agents or unique for an agent. Agents may cooperate with one another to facilitate their progresses. One of the fundamental challenges in such settings is that agents do not have a full knowledge over the environment and regarding their decision making processes, they might need to request other agents for a piece of information or service. The crucial issues are then how to rely on the information provided by other agents, how to consider the collected data, and how to select appropriate agents to ask for the required information. There are some proposals addressing how an agent can rely on other agents and how an agent can compute the overall opinion about a particular agent. In this context, the trust value reflects the extent to which agents can rely on other agents and the reputation value represents public opinion about a particular agent. Existing approaches for reliable information propagation fail to capture the dynamic relationships between agents and their influence on further decision making process. Therefore, these models fail to adapt agents to frequent environment changes. In general, a well-founded trust and reputation system that prevents malicious acts that are emerged by selfish agents is required for multi-agent systems. We propose a trust mechanism that measures and analyzes the reliability of agents cooperating with one another. This mechanism concentrates on the key attributes of the related agents and their relationships. We also measure and analyze the public reputation of agents in large-scale environments utilizing a sound reputation mechanism. In this mechanism, we aim at maintaining a public reputation assessment in which the public actions of agents are accurately under analysis. On top of the theoretical analysis, we experimentally validate our trust and reputation approaches through different simulations. Our preliminary results show that our approach outperforms current frameworks in providing accurate credibility measurements and maintaining accurate trust and reputation mechanisms

A Finite Difference Method for Off-fault Plasticity throughout the Earthquake Cycle

We have developed an efficient computational framework for simulating multiple earthquake cycles with off-fault plasticity. The method is developed for the classical antiplane problem of a vertical strike-slip fault governed by rate-and-state friction, with inertial effects captured through the radiationdamping approximation. Both rate-independent plasticity and viscoplasticity are considered, where stresses are constrained by a Drucker-Prager yield condition. The off-fault volume is discretized using finite differences and tectonic loading is imposed by displacing the remote side boundaries at a constant rate. Time-stepping combines an adaptive Runge-Kutta method with an incremental solution process which makes use of an elastoplastic tangent stiffness tensor and the return-mapping algorithm. Solutions are verified by convergence tests and comparison to a finite element solution. We quantify how viscosity, isotropic hardening, and cohesion affect the magnitude and off-fault extent of plastic strain that develops over many ruptures. If hardening is included, plastic strain saturates after the first event and the response during subsequent ruptures is effectively elastic. For viscoplasticity without hardening, however, successive ruptures continue to generate additional plastic strain. In all cases, coseismic slip in the shallow sub-surface is diminished compared to slip accumulated at depth during interseismic loading. The evolution of this slip deficit with each subsequent event, however, is dictated by the plasticity model. Integration of the off-fault plastic strain from the viscoplastic model reveals that a significant amount of tectonic off-set is accommodated by inelastic deformation (~0.1 m per rupture, or ~10% of the tectonic deformation budget)

Numerical Modeling of a Pile-Supported Wharf Subjected to Liquefaction-Induced Lateral Ground Deformations

Fully-coupled nonlinear dynamic analysis is increasingly used for assessing the seismic performance of pile-supported wharf structures subjected to liquefaction-induced lateral ground deformations. Several numerical challenges exist for analysis of this highly nonlinear soil-structure interaction, which require robust, yet practical, solutions that are validated with experimental data. This study presents a numerical model of a pile-supported wharf and evaluates the applicability of a soil constitutive model, and modeling assumptions and methods by using recorded data from a well-instrumented, large-scale centrifuge test. The objectives of this study include: (a) evaluating the performance of a recently developed pressure-dependent multi-yield surface constitutive soil model (PDMY03) to simulate the behavior of a liquefiable sand (b) assessing the effectiveness of a soil–pile interaction modeling approach in capturing the kinematic displacement demands on piles from a laterally spreading ground, and (c) evaluating the effectiveness and limitations of the 2D numerical model in approximating the 3D behavior of a wharf structure supported by multiple rows of piles, including the dynamic response of the centrifuge container. The implications of these assumptions and lessons learned from this study provide guidance for researcher modelers and practitioners for numerical modeling of similar soil–structure systems

Pile-Supported Wharves Subjected to Inertial Loads and Lateral Ground Deformations. II: Guidelines for Equivalent Static Analysis

An equivalent static analysis (ESA) procedure is proposed for the design of pile-supported wharves subjected to combined inertial and kinematic loads during earthquakes. The accuracy of the ESA procedure was evaluated against measurements from five large-scale centrifuge tests. The wharf structures in these tests were subjected to a suite of recorded ground motions and the associated superstructure inertia, as well as earthquake-induced slope deformations of varying magnitudes. It is shown that large bending moments at depths greater than 10 pile diameters were primarily induced by kinematic demands and can be estimated by applying soil displacements only (i.e., 100% kinematic). In contrast, the large bending moments at the pile head are primarily induced by wharf deck inertia and can be estimated by applying superstructure inertial loads at the pile head only (i.e., 100% inertial). Large bending moments at depths shallower than 10 pile diameters are affected by both inertial and kinematic loads; therefore, evaluation of pile performance should include soil displacements and a portion of the peak inertial load at the pile head that coincides with the peak kinematic loads. Ranges for inertial and kinematic load combinations in uncoupled analyses are provided for different soil profiles. The details on the back-calculated load combination factors are provided in the companion paper

Analyzing communities vs. single agent-based Web services: Trust perspectives

Gathering functionally similar agent-based Web services into communities has been proposed and promoted on many occasions. In this paper, we compare the performance of these communities with self-managed, single agent-based Web services from trust perspective. To this end, we deploy a reputation model that ranks communities and Web services with respect to different reputation parameters. By relating the parameters, we extend our discussion to analyze the beneficial cases and incentives for a single Web service to join a community even if this joining could negatively impact other parameters. Besides theoretical discussions of this analysis, we discuss the system implementation along with simulations that depict diverse parameters and system performance. © 2010 IEEE