Time Dependent Capacity Increase for Driven Pile in Cohesionless Soil

The increase in driven pile capacity with time is termed set-up. The mechanism contributing to this phenomenon is not yet fully understood. Moreover, a rational approach to account for the increase in driven pile capacity with time in design has not yet been developed. In this study, a database comprising of 55 pile load tests (static and dynamic tests) were collected from the current engineering literature. The piles were driven in cohesionless soils with sand relative density varying from loose to dense. The measured capacities of the database piles with time were correlated to pile characteristics and soil properties. Pile set-up was found to be a phenomenon related to an increase in pile shaft friction with time and increases with decreasing pile diameter. On the other hand, pile setup was found to increase with increasing pile penetration depth and thus with pile slenderness ratio. A new approach for the estimation of pile set-up in cohesionless soils is presented in this study. The new approach considers the effects of pile characteristics and soil properties. Comparison of predicted and measured pile set-up using the developed method in this study indicates reasonable agreement. Also, comparison of prediction using the new approach with those made using previously published methods indicates that the developed method in this study yields better results

Determination of Saline Soils Specific Gravity

The existence of salts as part of the solid phase of the soil or dissolved within the pore fluid may cause significant errors in the values of specific gravity of such soils by using conventional determination methods. Errors may arise from effects of wrong measurements of weights or volumes that take place due to dissolution of the salt during testing, precipitation during drying or dehydration of the crystals of certain salts such as gypsum. To overcome this confusion, the standard procedure for specific gravity determination is reconsidered and the calculation methods are reanalyzed. Suggestions for a more adequate procedure for gypseous or other types of saline soils are presented and corrections required for computations are derived

Seismicity of Jordan and Conterminous Countries

An up-to-date seismic hazard maps for Jordan and conterminous areas have been developed based on probabilistic approach. Such maps are intended to show the Peak Ground Acceleration (PGA) with 90% probability of not being exceeded in a life time of 50, 100, and 200 years, respectively. The computer program FRISK was used for estimating the PGA. A suitable attenuation equation reported in the literature, along with up-to-date earthquake catalogue including all the earthquake events that occurred in Jordan and neighboring countries, were considered in this study. Altogether, ten seismic zones as potential of earthquake activities are identified in the assessment of the seismic hazard maps. These are Aqaba Gulf fault, Wadi Araba fault, Dead Sea fault, Northern fault, SE-Mediterranean fault, Farah and Carmel faults, Wadi Sirhan fault, Karak-Fayha fault, Suez Gulf fault, and Cyprus zone fault

Deaggregation of Probabilistic Ground Motions for Selected Jordanian Cities

Probabilistic Seismic Hazard Analysis (PSHA) approach was adopted to investigate seismic hazard distribution across Jordan. Potential sources of seismic activities in the region were identified, and their earthquake recurrence relationships were developed from instrumental and historical data. Maps of peak ground acceleration and spectral accelerations (T=0.2 and T=1.0 sec.) of 2% and 10% probability of exceedance in 50 years were developed. This study deaggregated the PSHA results of 2% and 10% probability of exceedance in 50 years results of twelve Jordanian cities to help understand the relative control of these sources in terms of distances and magnitudes. Results indicated that seismic hazard across these cities is mainly controlled by area sources located along the Dead Sea Transform (DST) fault system. Cities located at short distances from the DST tend to show close deaggregation behavior. Some discrepancies may exist due to the proximity or remoteness of these cities relative to the DST seismic sources and local seismicity. The modal or most probable distance distribution indicated that the distance to the earthquake which contributes most to the hazard at each city is mainly controlled by shaking along faults associated with near seismic area sources. The influence of adjacent seismic sources to the seismic hazard of each city is more evident for the long period spectral acceleration. Distant sources, such as the eastern Mediterranean, Cyprus, Suez and the southern region of the Gulf of Aqaba are relatively low, but can not be neglected due to the intrinsic uncertainties and incomplete seismic data

Design of Geogrid Reinforced Earth Walls: Transition of Limits and Critical Surfaces

The majority of design approaches or methodologies for reinforced earth walls or slopes are based on separately investigating the internal and external stabilities of the system. The internal stability is examined by satisfying the local stability of reinforcements at each level based on the predetermined critical slip plane (line of maximums) and the tributary area of each reinforcing layer. Recent research aimed at incorporating the contributions of the various elements of reinforced earth walls, some of which are mostly based on statistical correlations. The German code of practice for design/analysis of reinforced earth walls and slopes offers slightly different methodology for analyzing the internal stability of the reinforcement. It is mainly based on investigating numerous circular and random slip surfaces, within and beyond the reinforcement zone (internal and external), while accommodating the axial (resistance) forces provided by all reinforcement layers intercepting these surfaces. This paper presents some of the technical and design considerations and possible improvements on design methodology for reinforced soil walls and slopes. Of particular interest is the use of the apparent cohesion concept in the design of geosynthetic reinforced soil systems and the transition of limit equilibrium states (mobilization of actual state of equilibrium critical surfaces instead of the presumed or predefined most critical surface) for reinforced earth walls. The equivalent cohesion concept was used to transform reinforced soil masses into equivalent cohesive soil masses with friction capacity. Cases of analyses with comparisons between reinforced soil walls and the equivalent cohesive masses were performed and the results revealed very similar results between the two systems in terms of the safety of the walls

NLFEA of Sulfate-Damaged Circular CFT Steel Columns Confined with CFRP Composites and Subjected to Axial and Cyclic Lateral Loads

It is rather costly and difficult to experimentally evaluate the performance of concrete-filled tubular (CFT) circular steel columns exposed to combined axial and cyclic lateral loads. This research paper uses the nonlinear finite element (NLFEA) technique to assess the influence of using carbon-fiber-reinforced polymer (CFRP) laminates on the structural response and failure mode of damaged-by-sulfate CFT circular steel columns. At the beginning, twenty-one CFT circular steel column models were devised and checked for soundness using the findings of previously conducted research. Next, the models were broadened to investigate how the models’ behavior was influenced by the CFRP number of layers and the level of sulfate damage. For experimental purposes, the numbers of CFRP layers were set to be zero, five, six, seven, eight, nine, and ten, while there were three levels of sulfate damage, namely: level 0 (undamaged), level 1 (73 days), and level 2 (123 days). Some of the models were left unconfined with CFRP wraps for comparison. The CFRP confinement was at the end of the models due to its importance regarding the models’ capacity of lateral load. The columns’ ends were confined to prevent the models from outward local buckling, which led to higher strength, bigger net drift, and enhanced energy dissipation. The NLFEA models were then appropriately modified and adjusted in accordance with credible previously conducted experimental research; after which, a parametric study was performed to investigate how the models’ behavior was affected by the number of CFRP layers and the level of axial load. The study found that the CFT circular steel column models’ performance significantly enhanced when the models were wrapped with five to ten CFRP layers. It must be mentioned, though, that using eight, nine, and ten CFRP layers gave almost similar results. In addition, the NLFEA results revealed that when the damaged-by-sulfate models were repaired externally with CFRP wraps, there was an improvement in the models’ cyclic behavior, as they showed a raise in the load capacity, an enhancement in the horizontal displacement, a greater displacement ductility, better energy dissipation, and little deterioration in secant stiffness. The study found that using wraps of CFRP proved a great efficiency with the change in the sulfate damage level

Cyclic Behavior of FRP Strengthened Beam-Column Joints under Various Concrete Damage Levels

This paper is intended to examine the efficiency of utilizing the FRP composite material with an externally bonded technique in enhancing the behavior of the damaged B-C joints and controlling their failure mode using the NLFEA approach. At first, the modeled Beam-Column joint was validated as per the previously-attained experimentally-attained results. Later, the model was widened to experiment with the impact of axial-column load and the concrete compressive strength on the reinforced and un-reinforced models with FRP. To run the experiment, there were three cases of applying the axial column load: no load applied (0%), applying 25%, applying 50%, and applying 75%, while the concrete compressive strength degradation level was (0% damage), (25% damage), and (50% damage). All models were evaluated for structural performance, considering: the failure mode, stresses distribution, and the ultimate capacities in pulling and pushing with its corresponding displacements. However, the horizontal load-displacement hysteretic loops and envelopes, stiffness degradation, displacement ductility, and energy dissipation were reported. The experimental results revealed that using FRP to externally-reinforce B-C joints improved overall cyclic performance, as the FRP caused a rise in the ultimate load capacity, horizontal displacement, ductility of displacement, and displacement energy dissipation, while it slowed down the stiffness degradation. In addition, the FRP material converted the failure mode of the region between the joint and column from brittle to ductile due to the formation of a plastic hinge only on the side of the beam when the axial column load exceeded 25%. It must be noticed that when the column’s axial load is less than 25%, the ultimate capacity of axial load and resultant deflection is solely improved. However, it has been stated that increasing the column’s axial loading by 25% increases the resulting stiffness degradation by 3% for undamaged joints, which further increases by 16% for each increased damage level. In contrast, the absorbed energy is increased by 170% under axial loading, increasing by 25%, which is reduced to only one-fourth under the various damage levels. Generally, the resulting observations help specialized engineers retrofit appropriate B-C joints in already-standing buildings due to their accuracy