Mounir Mabsout

Evaluation of Bond Strength of Steel Reinforcing Bars in Plain and Fiber-Reinforced Concrete

This study aimed to analytically evaluate the development/splice strength of reinforcing bars in tension by incorporating a local bond-stress slip law more accurately derived by using beam specimens. The influence of several parameters, such as concrete compressive strength, on the development and bond properties of reinforcing bars embedded in conventional concrete, and the effect of fiber reinforcement on bond performance in comparison with plain unconfined concrete and concrete confined by transverse reinforcement, were investigated. Based on results of this analytical study and available experimental data, a design expression was proposed to evaluate the contribution of steel fiber reinforcement to the development/splice strength of reinforcing bars in tension.

Response of Externally Post-Tensioned Continuous Members

Results from experimental and analytical evaluations of the behavior and strength characteristics of continuous concrete beams prestressed using external tendons are presented. Similarly to beams with internal unbonded tendons, the stresses in the prestressing steel at nominal flexural strength were below or slightly exceeded yield. As a result of the change in tendon eccentricity with increasing beam deflection, specimens with undeviated tendons mobilized relatively smaller load capacities and post-elastic deformations. Increasing the area of internal bonded reinforcement resulted in better crack distribution and, consequently, a more ductile mode of flexural failure. A comprehensive analytical model based on the concept of plastic hinge length was developed to predict the flexural response characteristics of continuous concrete members post-tensioned with external or internal unbonded tendons, with appropriate consideration given to the influence of the 2nd-order effects and the rotational capacity in the plastic region. The important parameters affecting the behavior are evaluated and discussed.

Pile driving by numerical cavity expansion

A cavity expansion procedure for the simulation of pile driving is presented and assessed in this paper. The analysis uses a non-linear finite-element model and the penetration of the pile into the soil is simulated by a radial opening of the soil around the pile. The case of a pile advanced by expansion will be compared to a similar pile subjected to computational driving (referred to, respectively, as ‘expanded’ and ‘driven’ piles for convenience). The state of stress and deformation, and the evolution of pore-water pressure in the soil will be monitored for the expanded and driven piles. Further computational driving will be applied to both cases and the pile response and soil resistance will be compared. The computational cost of advancing the pile by expansion will finally be investigated. Copyright

Finite Element Analysis of Concrete Box Culverts

This paper presents the finite element results of a parametric investigation of three precast concrete box culverts subject to various soil covers and loading conditions. The three culvert sizes had a constant rise of 8 ft (2.4m) and different span length of 12 ft, 18 ft, and 24 ft (3.6m, 5.4m, and 7.2m). Six possible soil covers were also considered (0, 2, 4, 6, 8, and 10 ft). As the soil depth increases, the wheel loads were projected on the top slab using ASTM C890 formula. Lateral earth pressure was applied on the vertical walls which depends on the depth of the box culvert. The finite element method was used to analyze the structural behavior of the three-dimensional box culvert under different loading conditions using SAP 2000. The culverts were modeled using SHELL elements with six degrees of freedom at each node. The FEA results were compared with AASHTO plane frame analysis. In addition to live loads, all structures were subjected to three independent load cases: (a) overburden pressure alone, (b) overburden plus lateral earth pressure, and (c) overburden plus lateral plus bearing pressure.

Influence of skew angle on live load moments in steel girder bridges

This paper presents the results of a parametric study evaluating the effect of skew angle on the wheel load distribution in steel girder highway bridges. The finite element method was used to investigate the effect of various parameters such as the span length, girder spacing, and skew angle, on simply supported, one-span, two-lane, three-lane and four-lane steel girder bridges. A total of 270 bridge cases were analyzed and subjected to AASHTO HS20 design trucks positioned on each bridge to produce maximum bending in the interior steel girders. A combination of five typical span lengths, three girder spacing, and six skew angles were used in evaluating bending moments in skewed steel girder bridges. The finite element results were used to calculate the maximum bending moment in steel girders due to the various skew angles and compared to the reference straight bridges, and then compared to the reduction factors used in AASHTO LRFD Bridge Design Specifications. The finite element results showed the reduction in bending moment for all skewed bridges up to 30 degrees can be neglected and such bridges can be designed as straight bridges. These results are consistent with the AASHTO Standard Specifications and the LRFD procedure by not specifying any reduction factor for bridges with skew angles up to 30 degrees. For highly skewed bridges and span length less than 80 ft (24 m), the finite element results showed a reduction in moment ranging between 10% and 20% for skew angles up to 40 degrees, and between 20% and 35% for skew angle up to 50 degrees. For practical application, a conservative reduction in girder bending moment of 15% is suggested for skew angles between 30 and 40 degrees and another conservative reduction in girder bending moment of 25% for bridges with skew angles between 40 and 50 degrees. Furthermore, the AASHTO LRFD reduction factors, ranging between 15% and 5%, were more conservative when compared with the finite element results for short-span bridges with high skew angles.

Nonlinear finite element analysis of upheaval buckling of buried offshore pipelines in medium dense sand with fines

Offshore pipelines that transport oil and gas in different areas of the world are often buried in trenches to provide stability and protection against upheaval buckling. Hydrocarbons in the pipeline are transported at high temperatures and pressures to facilitate flow and prevent potential solidification. Such conditions of transport, however, generate increases in axial compressive forces in the pipeline, which may lead to upward buckling (in the direction of the least soil resistance). Upheaval buckling can result in pipeline failure causing severe environmental and economic losses. The potential for upheaval buckling is mitigated by the resistance of the soil overlying the pipeline. This resistance is a function of several parameters. In this study, a series of 3D displacement-controlled finite element analyses were conducted using AbaqusTM to investigate the effects of pipeline diameter, pipeline embedment depth, and fines content on the soil resistance against uplift buckling. In the analyses, the offshore pipeline was assumed to be buried in medium dense sand with fines and was pulled upward along its entire length to simulate plane-strain conditions. The response of the pipeline was: (1) studied through the variation of the normalized uplift soil resistance with respect to normalized pipeline displacement, and (2) compared to the predicted response from available analytical resistance models. The results show that the uplift resistance, along with the normalized mobilization distance, depends on the pipeline diameter, embedment soil depth and fines content. Moreover, analytical design methods which assume mobilized soil blocks with inclined slip surfaces better capture the behavior observed in the numerical models, when compared to methods in which vertical slip surfaces are considered.

Normal Fault Movement Propagation in Overlying Seabed Deposits

This paper addresses the response of seabed sands subjected to underlying normal fault movement. This problem is relevant to the design of overlying offshore structures and subsea oil/gas pipelines connecting offshore platforms to the shoreline. The propagation of the faulting offset in seabed sediments is explored using 2D finite element modeling. Abaqus© is used as a numerical platform in modeling this complex problem, while accounting for nonlinear soil behavior with strain softening. Different dip angles and vertical fault displacements of up to 10% of the soil layer thickness were considered. The results include the effect of the relative density of the seabed sands on the extent and magnitude of ground surface deformations. The required bedrock displacement/offset for the rupture to reach the surface and the length and location of the distorted zone are also reported. The results show that the cases of loose sands and larger soil layer thicknesses result in larger distorted zones and that larger bedrock displacements are required for the fault base rupture to propagate to the surface. At low dip angles, graben formation is observed at small bedrock displacements. Based on the parametric analyses and results presented in this paper, observations related to the potential magnitudes and extents of surface deformations for various conditions of seabed densities and thicknesses are provided. These would be of importance in determining likely effects of distortion/loading on pipelines and offshore structures crossing the fault zone.

Uplift Resistance of Offshore Pipelines Subject to Upheaval Buckling

Offshore pipelines that transport oil and gas in different areas in the world are often buried in trenches to provide stability and protection against upheaval buckling. Hydrocarbons in the pipeline are transported at high temperatures and pressures to facilitate the oil flow and prevent its solidification. However, this mode of transport causes an increase in the axial compressive forces inside the pipeline which may lead to upward buckling in the direction of the least soil resistance. Upheaval buckling can result in pipeline failure causing severe environmental and economic losses. In this paper, a 3D parametric study of upheaval buckling of pipelines buried in medium dense sand with fines is performed using the finite element software Abaqus©. The effects of pipeline diameter, embedment depth ratio and diameter to wall thickness ratio on the soil resistance against uplift are investigated for pipeline pullout cases simulating plane strain conditions. The results are compared with the available analytical/empirical solutions for the uplift resistance. The results show that the uplift resistance depends in part on the pipeline diameter and embedment depth ratio. The available design methods which assume mobilized soil blocks above the pipeline with inclined slip surfaces better capture the behavior observed in the numerical models, as compared to those methods in which vertical slip surfaces are considered.

Finite element analysis of the propagation of Earth’s surface deformation as a consequence of normal dip-slip offshore fault rupture

This paper addresses the deformation response of seabed sands subject to underlying normal fault movement. This problem is relevant to the design of overlying offshore structures and subsea oil/gas pipelines connecting offshore platforms to the shoreline. The mechanism of the fault propagation in overlying seabed deposits is examined using 2D finite element modeling. Abaqus© is used as a numerical platform in modeling this complex problem, while accounting for nonlinear soil behavior with strain softening. Different dip angles and vertical fault displacements of up to 10% of the soil layer thickness were considered. The results include the effect of the relative density of the seabed sands and the soil layer thickness on the extent and magnitude of ground surface deformations. The required bedrock displacement/offset for the rupture to reach the surface and the length and location of the distorted zone are also investigated. Based on the parametric analyses and results presented in this paper, observations related to the potential magnitudes and extents of surface deformations for various conditions of seabed densities and thicknesses are provided. These would be of importance in determining likely effects of distortion/loading on pipelines and offshore structures crossing the fault zone.