Mohanad Alfach | City, University of London (original) (raw)

Videos by Mohanad Alfach

The First International Conference in Construction Engineering: Towards more Sustainable Structu... more The First International Conference in Construction Engineering:
Towards more Sustainable Structures (ICCE 2021)
Sunday, November 28, 2021

6 views

Papers by Mohanad Alfach

Studia Geotechnica et Mechanica, Mar 1, 2024

This paper explores the impact of height ratios on the seismic Structure-Soil-Structure Interacti... more This paper explores the impact of height ratios on the seismic Structure-Soil-Structure Interaction (SSSI) for three adjacent bridges with varying superstructure masses (Mst
= 350, 1050, 350 t) through 3D numerical simulations. Acomprehensive series of numerical analyses has been conducted across different height ratios (R = 1,1.1, 1.15, 1.2, 1.25, 1.5, 2, and 3) to assess their influence on superstructure acceleration and the internal forces within the foundation piles. The bridges under investigation are supported by groups of piles embedded in nonlinear clay. The numerical simulations were executed using fast Lagrangian analysis of continua in three dimensions (FLAC 3D), a three-dimensional finite differences modeling software. The findings revealed that variations in mass ratios significantly impact the SSSI effects on superstructure acceleration and pile internal forces. Notably, adverse effects were more pronounced for mass ratios of R = 1.1 and 1.2, leading to an increase in bending moment, shear force, and superstructure acceleration by up to 237.8%, 291.4%, and 70.33%, respectively. In contrast, a mass ratio of R = 3 resulted in a decrease in bending
moment, shear force, and superstructure acceleration by up to 72%, 82.14%, and 81.13%, respectively. This implies that a careful arrangement of adjacent structures with different masses can be employed effectively to manage the (SSSI) effects.

Seismic Structure-Soil-Structure Interaction (SSSI) between piled neighboring bridges: Influence of height ratio, 2024

This paper explores the impact of height ratios on the seismic Structure-Soil-Structure Interacti... more This paper explores the impact of height ratios on the seismic Structure-Soil-Structure Interaction (SSSI) for three adjacent bridges with varying superstructure masses (M st = 350, 1050, 350 t) through 3D numerical simulations. A comprehensive series of numerical analyses has been conducted across different height ratios (R = 1, 1.1, 1.15, 1.2, 1.25, 1.5, 2, and 3) to assess their influence on superstructure acceleration and the internal forces within the foundation piles. The bridges under investigation are supported by groups of piles embedded in nonlinear clay. The numerical simulations were executed using fast Lagrangian analysis of continua in three dimensions (FLAC 3D), a three-dimensional finite differences modeling software. The findings revealed that variations in mass ratios significantly impact the SSSI effects on superstructure acceleration and pile internal forces. Notably, adverse effects were more pronounced for mass ratios of R = 1.1 and 1.2, leading to an increase in bending moment, shear force, and superstructure acceleration by up to 237.8%, 291.4%, and 70.33%, respectively. In contrast, a mass ratio of R = 3 resulted in a decrease in bending moment, shear force, and superstructure acceleration by up to 72%, 82.14%, and 81.13%, respectively. This implies that a careful arrangement of adjacent structures with different masses can be employed effectively to manage the (SSSI) effects.

Geomechanics and Geoengineering, Jun 7, 2021

Structure-soil-structure interaction between adjacent structures, which may occur in densely popu... more Structure-soil-structure interaction between adjacent structures, which may occur in densely populated urban areas, has received little attention compared to the soil-structure interaction of single isolated structures. Additionally, recent earthquakes in/near such areas (e.g. the Christchurch series, 2010-2011) have shown that large motions can be followed by strong aftershocks. In this paper, the seismic behaviour of isolated structures and pairs of adjacent structures under a sequence of strong ground motions has been investigated using a combination of centrifuge and finite-element modelling. The latter utilised an advanced constitutive model that can be parameterised from routine test data, making it suitable for use in routine design. The finite-element models were shown to accurately simulate the centrifuge-measured response (in terms of surface ground motion and structural sway, settlement and rotation) even after multiple strong aftershocks, so long as the buildings' initial conditions were reproduced accurately. For the case of a building structure with a close neighbour, structural drift and co-seismic settlement could be reduced or increased as a result of structure-soil-structure interaction, depending chiefly on the properties of the adjacent structure. This suggests that careful arrangement of adjacent structures and specification of their properties could be used to control the effects of structure-soil-structure interaction. In all cases where adjacent structures were present, permanent rotation (structural tilt) was observed to increase significantly, demonstrating the importance of considering structure-soil-structure interaction in assessing the seismic performance of structures.

Geotechnical and Geological Engineering

Case Studies in Construction Materials, 2022

Géotechnique, 2015

Structure–soil–structure interaction between adjacent structures, which may occur in densely popu... more Structure–soil–structure interaction between adjacent structures, which may occur in densely populated urban areas, has received little attention compared to the soil–structure interaction of single isolated structures. Additionally, recent earthquakes in/near such areas (e.g. the Christchurch series, 2010–2011) have shown that large motions can be followed by strong aftershocks. In this paper, the seismic behaviour of isolated structures and pairs of adjacent structures under a sequence of strong ground motions has been investigated using a combination of centrifuge and finite-element modelling. The latter utilised an advanced constitutive model that can be parameterised from routine test data, making it suitable for use in routine design. The finite-element models were shown to accurately simulate the centrifuge-measured response (in terms of surface ground motion and structural sway, settlement and rotation) even after multiple strong aftershocks, so long as the buildings' in...

Asian Journal of Civil Engineering, 2021

This study evaluates the dynamic behavior and performance of vital reinforced concrete (RC) publi... more This study evaluates the dynamic behavior and performance of vital reinforced concrete (RC) public building [Ministry of Higher Education (MHE)] designed in compliance with the old Syrian (non-seismic) building code. The real non-linear dynamic behavior of the MHE building has been checked by detailed dynamic numerical analyses (finite elements method—FEM) validated by a series of ambient noise measurements carried out on-site. The modeling approach for the thorough 3D dynamic analyses of the (RC) MHE building has been developed to be able to investigate the actual non-linear dynamic performance of widespread range of RC structures, providing the opportunity to set up a reliable detailed methodology to assess the real dynamic performance of the old vital structures designed according to the old Syrian (non-seismic) building code from the new seismic requirements perspective. The results of the frequency analyses, the nonlinear time history, and the experimental measurements have sho...

Communications in Computer and Information Science, 2020

This paper presents a three-dimensional numerical model of soil-damaged piles-bridge interaction ... more This paper presents a three-dimensional numerical model of soil-damaged piles-bridge interaction under seismic loading. This study focuses on the effect of developing plastic hinges in piles' foundation on the seismic behavior of the system. Several field investigations on seismic damages due to recent strong earthquakes have confirmed the decisive role of the plastic hinges in the piles in the seismic behavior of the system. In particular, this study is interested in evaluating the proposed approach for strengthening the system of soil-damaged pilesbridge. The proposed approach is based on using micropiles significantly promoting the flexibility and ductility of the system. This study was carried out using a three-dimensional finite differences' modeling program (FLAC 3D). The results confirmed the considerable effect of developing concrete plasticity in the piles' foundation, which reflects in changing the distribution of internal forces between the piles. Results show the efficiency of using micropiles as a reinforcement system. The detailed analysis of the micropiles' parameters shows a slight effect of pile-micropile spacing. The use of inclined micropiles leads to attenuation of internal forces induced in the piles and the micropiles themselves.

This paper presents a detailed analysis of the influence of plasticity on the seismic response of... more This paper presents a detailed analysis of the influence of plasticity on the seismic response of pile foundations. Since soils exhibit nonlinear and irreversible behaviour, it is of major interest to consider plasticity in the design of pile foundations for structures which may be subjected to severe earthquake loading. The study is carried out using a full three-dimensional finite difference modeling using a real earthquake record. The influence of soil plasticity is investigated on the seismic response of soil-pile-structure system for two idealized soil deposits: cohesive and frictional soils. Analyses provide valuable information on the influence of plasticity on the seismic response of soil-pile-structure systems. They show that the soil state in the vicinity of piles head dominates the piles response and may lead to higher deflection and bending stresses.

The present study assesses the effect of Structure-Soil-Structure-Interaction (SSSI) on the seism... more The present study assesses the effect of Structure-Soil-Structure-Interaction (SSSI) on the seismic behavior of three dissimilar adjacent bridges by comparing their seismic responses with the seismic response of the isolated bridge including Soil-Structure-Interaction (SSI). To this end, an extensive series of numerical analyses have been carried out to elicit the effects of Structure-Soil-Structure-Interaction (SSSI) on the seismic behavior of three dissimilar bridges with different superstructure masses. The studied bridges are based on groups of piles founded in nonlinear clay. A parametric study has been performed for configurations of three dissimilar bridges with superstructure masses ratios of 200% and 300%, concentrating on the influence of the inter-bridge spacing, and the geometrical position of the bridges towards each other and towards the seismic excitation direction. The numerical analyses have been conducted using a three-dimensional finite difference modeling softwar...

New approach for computing damage parameters evolution in plastic damage model for concrete, 2021

The Damage Plastic Model is one of the most widespread models used to simulate the real behavior ... more The Damage Plastic Model is one of the most widespread models used to simulate the real behavior of concrete. The high reliability of this model could be attributed to its ability to take into consideration the elastic stiffness degradation induced by plastic straining as well as the stiffness recovery effects under cyclic loading. This model has been implemented in ABAQUS under the name of Concrete Damaged Plasticity Model (CDPM). Nevertheless, the use of CDPM in ABAQUS is very sensitive due to the high complexity of the calibration process of comparing the model parameters with experimental data, particularly, the stress-inelastic strain diagrams and the damage parameters evolution. The main aim of this research is to develop a new methodology to facilitate the use of this model without the need to calibrate the stress-inelastic strain diagrams and the damage parameters evolution with experimental results. This methodology is based on Lubliner formulas to identify the stress-inelastic strain diagrams, and on Alfarah formulas to evaluate the damage parameters evolution. A new algorithm has been developed to determine the dimensionless coefficients of Lubliner and Alfarah formulas according to the Model Code recommendations. This algorithm has been implemented in developed finite element code where the results have been validated by comparing with experimental results and closed-form solutions.

Journal of Civil & Environmental Engineering

Post-seismic observations of recent devastating earthquakes have shown that the nonlinear behavio... more Post-seismic observations of recent devastating earthquakes have shown that the nonlinear behavior of the soil plays an essential and definitive role in development the damage to the system of soil-piles-structure during the earthquake. Similarly, slips or collapse the soil-piles interface may cause harmful ruptures. Consequently, an analysis of these problems is necessary to take into account the non-linearity of the soil and the possibility of a slip or collapse at the interface of soil-pile under intensive seismic loading. This study aims to investigate these interaction aspects for soil-piles-structure under real earthquake record using a global approach with a three-dimensional finite difference code-FLAC 3D (Fast Lagrangian analysis of continua in 3 dimensions). The results confirm that the non-linearity of soil and soil-pile interface has a great influence on the response of piles and structure. They show that the consideration of the plasticity of the soil leads to attenuation of efforts, especially for soft loose soils. The simulation carried out in this study illustrate that the use of weak soil-pile interface leads to an increase of bending moment accompanied by a reduction of shear and normal forces in the piles. While, for a medium or high resistance interface, the efforts induced in the piles approaching of those induced in the case of perfect contact.

Geotechnical Research

This paper presents a detailed analysis of the effect of oil contamination on the geotechnical be... more This paper presents a detailed analysis of the effect of oil contamination on the geotechnical behaviour of bridge pile foundations, focusing on the influence of soil type, oil-contamination intensity and oil-contamination depth. A thorough parametric study of these dominant parameters was carried out through numerical analyses that were performed using Flac3D software. The analyses were designed using three types of soils: poorly graded sand (SP), silty sand (SM) and kaolinite clay. Oil contamination degrades the geotechnical behaviour of bridge pile foundations. Soil type has a clear effect on the internal forces induced in the piles, with maximum normal forces occurring in SP, the maximum bending moment in kaolinite clay and maximum shear forces in SM. The variation of oil-contamination intensity in the soil changes the induced internal forces in the piles by ratios increasing to 40, 34 and 20% of the bending moment, the shear forces and the normal forces, respectively. However, the alterations in the displacements of the soil and the piles are more significant, with ratios up to 150%. In contrast, the oil-contamination depth has a limited effect on the internal force of the pile (up to 4%) but has a considerable effect on the displacement of the foundation.

Geomechanics and Geoengineering

Jordan Journal of Civil Engineering, 2012

Geotechnical Research

Dynamic behavior assessment of public buildings in Syria using non‑linear time‑history analysis and ambient noise measurements: a case study, 2021

This study evaluates the dynamic behavior and performance of vital reinforced concrete (RC) publi... more This study evaluates the dynamic behavior and performance of vital reinforced concrete (RC) public building [Ministry of Higher Education (MHE)] designed in compliance with the old Syrian (non-seismic) building code. The real non-linear dynamic behavior of the MHE building has been checked by detailed dynamic numerical analyses (finite elements method-FEM) validated by a series of ambient noise measurements carried out on-site. The modeling approach for the thorough 3D dynamic analyses of the (RC) MHE building has been developed to be able to investigate the actual non-linear dynamic performance of widespread range of RC structures, providing the opportunity to set up a reliable detailed methodology to assess the real dynamic performance of the old vital structures designed according to the old Syrian (non-seismic) building code from the new seismic requirements perspective. The results of the frequency analyses, the nonlinear time history, and the experimental measurements have shown an excellent agreement. The study showed that the modeling approach by the FEM is reliable for predicting the actual dynamic behavior of RC structures, but it is very sensitive to the modeling assumptions. Furthermore, the dynamic performance analyses have revealed unsymmetrical behavior of the east-west wings about the Y-axis which could be attributed to the inefficient seismic rehabilitation executed in 2001.

Recycling of Pavement materials

التصميم‬ ‫لطبقات‬ ‫االنشائي‬ ‫ن‬ ‫المر‬ ‫الرصف‬ ‫باستخدام‬ ‫األشتو‬ ‫طريقة‬ FLEXIBLE PAVEMENT LAY... more التصميم‬ ‫لطبقات‬ ‫االنشائي‬ ‫ن‬ ‫المر‬ ‫الرصف‬ ‫باستخدام‬ ‫األشتو‬ ‫طريقة‬ FLEXIBLE PAVEMENT LAYERS DESIGN BY USING AASHTO METHOD

6 views

Studia Geotechnica et Mechanica, Mar 1, 2024

Seismic Structure-Soil-Structure Interaction (SSSI) between piled neighboring bridges: Influence of height ratio, 2024

This paper explores the impact of height ratios on the seismic Structure-Soil-Structure Interacti... more This paper explores the impact of height ratios on the seismic Structure-Soil-Structure Interaction (SSSI) for three adjacent bridges with varying superstructure masses (M st = 350, 1050, 350 t) through 3D numerical simulations. A comprehensive series of numerical analyses has been conducted across different height ratios (R = 1, 1.1, 1.15, 1.2, 1.25, 1.5, 2, and 3) to assess their influence on superstructure acceleration and the internal forces within the foundation piles. The bridges under investigation are supported by groups of piles embedded in nonlinear clay. The numerical simulations were executed using fast Lagrangian analysis of continua in three dimensions (FLAC 3D), a three-dimensional finite differences modeling software. The findings revealed that variations in mass ratios significantly impact the SSSI effects on superstructure acceleration and pile internal forces. Notably, adverse effects were more pronounced for mass ratios of R = 1.1 and 1.2, leading to an increase in bending moment, shear force, and superstructure acceleration by up to 237.8%, 291.4%, and 70.33%, respectively. In contrast, a mass ratio of R = 3 resulted in a decrease in bending moment, shear force, and superstructure acceleration by up to 72%, 82.14%, and 81.13%, respectively. This implies that a careful arrangement of adjacent structures with different masses can be employed effectively to manage the (SSSI) effects.

Geomechanics and Geoengineering, Jun 7, 2021

Geotechnical and Geological Engineering

Case Studies in Construction Materials, 2022

Géotechnique, 2015

Asian Journal of Civil Engineering, 2021

Communications in Computer and Information Science, 2020

New approach for computing damage parameters evolution in plastic damage model for concrete, 2021

Journal of Civil & Environmental Engineering

Geotechnical Research

Geomechanics and Geoengineering

Jordan Journal of Civil Engineering, 2012

Geotechnical Research

Dynamic behavior assessment of public buildings in Syria using non‑linear time‑history analysis and ambient noise measurements: a case study, 2021

This study evaluates the dynamic behavior and performance of vital reinforced concrete (RC) publi... more This study evaluates the dynamic behavior and performance of vital reinforced concrete (RC) public building [Ministry of Higher Education (MHE)] designed in compliance with the old Syrian (non-seismic) building code. The real non-linear dynamic behavior of the MHE building has been checked by detailed dynamic numerical analyses (finite elements method-FEM) validated by a series of ambient noise measurements carried out on-site. The modeling approach for the thorough 3D dynamic analyses of the (RC) MHE building has been developed to be able to investigate the actual non-linear dynamic performance of widespread range of RC structures, providing the opportunity to set up a reliable detailed methodology to assess the real dynamic performance of the old vital structures designed according to the old Syrian (non-seismic) building code from the new seismic requirements perspective. The results of the frequency analyses, the nonlinear time history, and the experimental measurements have shown an excellent agreement. The study showed that the modeling approach by the FEM is reliable for predicting the actual dynamic behavior of RC structures, but it is very sensitive to the modeling assumptions. Furthermore, the dynamic performance analyses have revealed unsymmetrical behavior of the east-west wings about the Y-axis which could be attributed to the inefficient seismic rehabilitation executed in 2001.

Recycling of Pavement materials

تأثير الحمولات الزائدة على شبكة الطرق السورية و طرق معالجتها - Overload Axles effects on the Syrian Highways net

تأثير الحمولات الزائدة على شبكة الطرق السورية و طرق معالجتها - Overload Axles effects on the Syri... more تأثير الحمولات الزائدة على شبكة الطرق السورية و طرق معالجتها - Overload Axles effects on the Syrian Highways net

Offshore Wind Turbines (OWT) - Renewable energy

After this lesson, students should be able to: • Define engineering stress, engineering strain, P... more After this lesson, students should be able to: • Define engineering stress, engineering strain, Poisson's ratio and modulus of elasticity. • Explain a typical engineering stress-strain diagram of an elastic material and its important features. • Determine elastic modulus, yield strength, and tensile strength from an engineering stress-strain diagram. • Understanding the reasons of material failure.

After this lesson, students should be able to: • Classifying the materials in different classes (... more After this lesson, students should be able to: • Classifying the materials in different classes (natural materials, metals, polymers, ceramics and glasses, and composites) according to their essential properties. • Understanding the factors that affect the properties of materials. • Define the essential materials properties. • Explain a typical engineering stress-strain diagram of material and its important features. • Determine elastic modulus, yield strength, and tensile strength from an engineering stress-strain diagram • Understanding the materials failure and degradation mechanisms. • Materials selection criteria for use in civil engineering design

Seismic Geotechnical Engineering Problems