Documents disponibles écrits par cet auteur

Alternative strategies to enhance the seismic performance of reinforced concrete-block shear wall systems / Shedid, Marwan T. in Journal of structural engineering, Vol. 136 N° 6 (Juin 2010) 

Public ISBD [article]  in Journal of structural engineering > Vol. 136 N° 6 (Juin 2010) . - pp. 676-689 Titre : Alternative strategies to enhance the seismic performance of reinforced concrete-block shear wall systems Type de document : texte imprimé Auteurs : Shedid, Marwan T., Auteur ; El-Dakhakhni, Wael W., Auteur ; Drysdale, Robert G., Auteur Année de publication : 2011 Article en page(s) : pp. 676-689 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Concrete  masonry  Cyclic  loads  Ductility  Experimental  tests  Flanges  Seismic  tests  Shear  walls Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : In this paper, seven reinforced concrete-block shear walls with aspect ratios of 1.5 and 2.2 (two- and three-storey high) were tested under displacement-controlled cyclic loading. The response of rectangular, flanged, and end-confined walls, designed to have the same lateral resistance when subjected to the same axial load, is discussed. In general, high levels of ductility accompanied by relatively small strength degradation were observed in all walls with a significant increase in ductility and displacement capabilities for the flanged and end-confined walls compared to the rectangular ones. For both aspect ratios evaluated, the drift levels at 20% strength degradation were 1.0, 1.5, and 2.2% corresponding to the rectangular, the flanged, and the end-confined walls, respectively. The ductility values of the proposed flanged and end-confined walls were, respectively, 1.5 and 2 times those of their rectangular wall counterparts (with the same overall length and aspect ratio). In addition to the enhanced ductility, a saving of more than 40% in the amount of vertical reinforcement was achieved using the proposed alternative strategies while maintaining the same lateral wall resistance. Existing design clauses were used to predict the wall capacities using the American and the Canadian masonry codes and showed excellent agreement. This will facilitate adoption of the new construction categories with minimal modifications to existing code clauses. The test results indicate that higher ductility than the currently endorsed values by North American codes should be used for rectangular walls. Moreover, higher values should be expected when the proposed strategies are adopted which would significantly reduce the seismic demand on reinforced concrete-block shear wall construction. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v136/i6/p676_s1?isAuthorized=no [article] Alternative strategies to enhance the seismic performance of reinforced concrete-block shear wall systems [texte imprimé] / Shedid, Marwan T., Auteur ; El-Dakhakhni, Wael W., Auteur ; Drysdale, Robert G., Auteur . - 2011 . - pp. 676-689. Génie Civil Langues : Anglais (eng) in Journal of structural engineering > Vol. 136 N° 6 (Juin 2010) . - pp. 676-689 Mots-clés : Concrete  masonry  Cyclic  loads  Ductility  Experimental  tests  Flanges  Seismic  tests  Shear  walls Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : In this paper, seven reinforced concrete-block shear walls with aspect ratios of 1.5 and 2.2 (two- and three-storey high) were tested under displacement-controlled cyclic loading. The response of rectangular, flanged, and end-confined walls, designed to have the same lateral resistance when subjected to the same axial load, is discussed. In general, high levels of ductility accompanied by relatively small strength degradation were observed in all walls with a significant increase in ductility and displacement capabilities for the flanged and end-confined walls compared to the rectangular ones. For both aspect ratios evaluated, the drift levels at 20% strength degradation were 1.0, 1.5, and 2.2% corresponding to the rectangular, the flanged, and the end-confined walls, respectively. The ductility values of the proposed flanged and end-confined walls were, respectively, 1.5 and 2 times those of their rectangular wall counterparts (with the same overall length and aspect ratio). In addition to the enhanced ductility, a saving of more than 40% in the amount of vertical reinforcement was achieved using the proposed alternative strategies while maintaining the same lateral wall resistance. Existing design clauses were used to predict the wall capacities using the American and the Canadian masonry codes and showed excellent agreement. This will facilitate adoption of the new construction categories with minimal modifications to existing code clauses. The test results indicate that higher ductility than the currently endorsed values by North American codes should be used for rectangular walls. Moreover, higher values should be expected when the proposed strategies are adopted which would significantly reduce the seismic demand on reinforced concrete-block shear wall construction. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v136/i6/p676_s1?isAuthorized=no

Characteristics of rectangular, flanged, and end-confined reinforced concrete masonry shear walls for seismic design / Shedid, Marwan T. in Journal of structural engineering, Vol. 136 N° 12 (Décembre 2010) 

Public ISBD [article]  in Journal of structural engineering > Vol. 136 N° 12 (Décembre 2010) . - pp. 1471-1482 Titre : Characteristics of rectangular, flanged, and end-confined reinforced concrete masonry shear walls for seismic design Type de document : texte imprimé Auteurs : Shedid, Marwan T., Auteur ; El-Dakhakhni, Wael W., Auteur ; Drysdale, Robert G., Auteur Année de publication : 2011 Article en page(s) : pp. 1471-1482 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Concrete  masonry  Cyclic  loads  Ductility  Experimental  tests  Flanges  Seismic  tests  Shear  walls Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper contains detailed analyses of an experimental study conducted to evaluate the ductility, stiffness degradation and energy dissipation characteristics of rectangular, flanged, and end-confined reinforced masonry (RM) shear walls failing in flexure. The test program consisted of seven two- and three-story RM shear walls, with aspect ratios of 1.5 and 2.2, tested under reversed cyclic lateral displacements simulating seismic loading effects. Documentation of the compressive strains at the wall toes, wall base curvatures, and ductility levels attained are presented. The paper focuses on determining the extent of plasticity over the wall height, evaluating the contribution of flexure and shear deformations to the overall wall lateral displacements, identifying the trend of stiffness degradation, and quantifying the amount of energy dissipation. The rectangular walls displacement predictions at ultimate loads using Canadian Standards Association (CSA) S304.1 were in better agreement with the experimental results compared to the Masonry Standards Joint Committee (MSJC) code predictions. However, both the MSJC code and the CSA S304.1 significantly overestimated the test results for the flanged and end-confined walls. Analysis of the measured displacements showed that the contribution of shear displacement to the overall wall displacement was, on average, 21 and 25% of the total displacement for the walls with aspect ratio of 2.2 and 1.5, respectively. The relationship between the energy dissipation and the ratio of the postyield to the yield displacements was found to be almost linear for the test walls. In addition, the wall stiffnesses degraded rapidly to about 60% of their gross stiffness at very low drift levels (0.1% drift). Measured compressive strain at the wall toes were almost double those specified in both North American codes. Extent of plasticity over the wall height was about 75% of the wall length. The data presented in this paper is expected to facilitate better understanding of RM wall behavior under in-plane load to researchers, practicing engineers, and code developers. This study aimed at presenting the flanged and end-confined categories as cost-effective alternatives to enhance the seismic performance of midrise RM construction in North America. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v136/i12/p1471_s1?isAuthorized=no [article] Characteristics of rectangular, flanged, and end-confined reinforced concrete masonry shear walls for seismic design [texte imprimé] / Shedid, Marwan T., Auteur ; El-Dakhakhni, Wael W., Auteur ; Drysdale, Robert G., Auteur . - 2011 . - pp. 1471-1482. Génie Civil Langues : Anglais (eng) in Journal of structural engineering > Vol. 136 N° 12 (Décembre 2010) . - pp. 1471-1482 Mots-clés : Concrete  masonry  Cyclic  loads  Ductility  Experimental  tests  Flanges  Seismic  tests  Shear  walls Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper contains detailed analyses of an experimental study conducted to evaluate the ductility, stiffness degradation and energy dissipation characteristics of rectangular, flanged, and end-confined reinforced masonry (RM) shear walls failing in flexure. The test program consisted of seven two- and three-story RM shear walls, with aspect ratios of 1.5 and 2.2, tested under reversed cyclic lateral displacements simulating seismic loading effects. Documentation of the compressive strains at the wall toes, wall base curvatures, and ductility levels attained are presented. The paper focuses on determining the extent of plasticity over the wall height, evaluating the contribution of flexure and shear deformations to the overall wall lateral displacements, identifying the trend of stiffness degradation, and quantifying the amount of energy dissipation. The rectangular walls displacement predictions at ultimate loads using Canadian Standards Association (CSA) S304.1 were in better agreement with the experimental results compared to the Masonry Standards Joint Committee (MSJC) code predictions. However, both the MSJC code and the CSA S304.1 significantly overestimated the test results for the flanged and end-confined walls. Analysis of the measured displacements showed that the contribution of shear displacement to the overall wall displacement was, on average, 21 and 25% of the total displacement for the walls with aspect ratio of 2.2 and 1.5, respectively. The relationship between the energy dissipation and the ratio of the postyield to the yield displacements was found to be almost linear for the test walls. In addition, the wall stiffnesses degraded rapidly to about 60% of their gross stiffness at very low drift levels (0.1% drift). Measured compressive strain at the wall toes were almost double those specified in both North American codes. Extent of plasticity over the wall height was about 75% of the wall length. The data presented in this paper is expected to facilitate better understanding of RM wall behavior under in-plane load to researchers, practicing engineers, and code developers. This study aimed at presenting the flanged and end-confined categories as cost-effective alternatives to enhance the seismic performance of midrise RM construction in North America. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v136/i12/p1471_s1?isAuthorized=no

Detection of ungrouted cells in concrete masonry constructions using a dielectric variation approach / El-Dakhakhni, Wael W. in Journal of engineering mechanics, Vol. 136 N° 4 (Avril 2010) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 136 N° 4 (Avril 2010) . - pp. 438-447 Titre : Detection of ungrouted cells in concrete masonry constructions using a dielectric variation approach Type de document : texte imprimé Auteurs : El-Dakhakhni, Wael W., Auteur ; Nassr, Amr A., Auteur ; Shedid, Marwan T., Auteur Article en page(s) : pp. 438-447 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Walls  Masonry  Grouting  Probe  instruments  Damage  Measurement  Nondestructive  tests  Concrete  construction. Résumé : n this study, a new technique for detecting ungrouted cells in concrete block masonry constructions was developed. The concept, based on detecting the local dielectric permittivity variations, was employed to design coplanar capacitance sensors with high sensitivities to detect such construction defects. An analytical model and finite element simulations were used to assess the influence of the sensor geometrical parameters on the sensor signals and to optimize the sensor design. To experimentally verify the model, the dielectric properties of various materials involved in concrete masonry walls were measured. In addition, a masonry wall containing predetermined grouted and ungrouted cells was constructed and inspected using the developed sensors in a laboratory setting. Moreover, different capacitance sensors were designed and compared with respect to their sensitivity, signal-to-noise ratio, and coefficient of variation of the inspected measurements. Excellent agreements were found between the experimental capacitance signal response parameters and those predicted by the analytical and finite element models. The proposed sensor design, coupled with a commercially available portable capacitance meter, would facilitate employing this technique in the field for rapid inspection of masonry structures without the need for sophisticated data analyses usually required by other more expensive and time consuming methods. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JENMDT&CURRENT=null [...] [article] Detection of ungrouted cells in concrete masonry constructions using a dielectric variation approach [texte imprimé] / El-Dakhakhni, Wael W., Auteur ; Nassr, Amr A., Auteur ; Shedid, Marwan T., Auteur . - pp. 438-447. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 136 N° 4 (Avril 2010) . - pp. 438-447 Mots-clés : Walls  Masonry  Grouting  Probe  instruments  Damage  Measurement  Nondestructive  tests  Concrete  construction. Résumé : n this study, a new technique for detecting ungrouted cells in concrete block masonry constructions was developed. The concept, based on detecting the local dielectric permittivity variations, was employed to design coplanar capacitance sensors with high sensitivities to detect such construction defects. An analytical model and finite element simulations were used to assess the influence of the sensor geometrical parameters on the sensor signals and to optimize the sensor design. To experimentally verify the model, the dielectric properties of various materials involved in concrete masonry walls were measured. In addition, a masonry wall containing predetermined grouted and ungrouted cells was constructed and inspected using the developed sensors in a laboratory setting. Moreover, different capacitance sensors were designed and compared with respect to their sensitivity, signal-to-noise ratio, and coefficient of variation of the inspected measurements. Excellent agreements were found between the experimental capacitance signal response parameters and those predicted by the analytical and finite element models. The proposed sensor design, coupled with a commercially available portable capacitance meter, would facilitate employing this technique in the field for rapid inspection of masonry structures without the need for sophisticated data analyses usually required by other more expensive and time consuming methods. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JENMDT&CURRENT=null [...]

Force- and displacement-based seismic performance parameters for reinforced masonry structural walls with boundary elements / Bennett R. Banting in Journal of structural engineering, Vol. 138 N° 12 (Décembre 2012) 

Public ISBD [article]  in Journal of structural engineering > Vol. 138 N° 12 (Décembre 2012) . - pp. 1477–1491 Titre : Force- and displacement-based seismic performance parameters for reinforced masonry structural walls with boundary elements Type de document : texte imprimé Auteurs : Bennett R. Banting, Auteur ; El-Dakhakhni, Wael W., Auteur Année de publication : 2013 Article en page(s) : pp. 1477–1491 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Cyclic  loads  Reinforced  masonry  Seismic  performance  Structural  walls  Wall  confinement Résumé : There is a need to evaluate existing, and introduce new, masonry construction techniques within a performance-based seismic design context to advance their adoption in the next generation of seismic design codes in North America. In this regard, a reinforced masonry (RM) structural wall system that incorporates confining boundary elements in the plastic hinge region presently lacks specific design requirements in the Masonry Standards Joint Committee and Canadian Standards Association S304.1 design codes. In addition, RM structural wall systems are omitted completely from the plan to develop a new performance-based seismic design methodology laid out by FEMA 445. This paper presents experimental results of four specially detailed RM structural walls subjected to fully reversed cycles of displacement-controlled loading as tested by the authors. In addition, the resulting analysis also includes one wall from a previous study for comparison purposes. All walls were detailed with lateral reinforcing ties confining a grouted core and four vertical reinforcement bars located at each of the wall ends. The design and detailing of the walls represented a range of parameters that would be anticipated to vary within low-to-medium-rise RM buildings. Each of the half-scale walls had overall dimensions of 1.8×4.0 m but varied by the level of applied axial load, the presence of interstory floor slabs, and the presence of confining boundary elements above the first-story height. The results of this experimental program indicate that boundary elements delayed the onset of buckling in the vertical reinforcement and reduced the impact of face-shell spalling on overall wall strength degradation. At 20% degradation from ultimate strength, the top drifts ranged from 1.82 to 3.73% and the displacement ductilities ranged from 6.6 to 15.2. This study is the first of a series of studies at McMaster University currently focused on introducing a broad set of experimental evidence aiming at establishing a new category of RM seismic force resisting systems in North American building codes. ISSN : 0733-9445 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29ST.1943-541X.0000572 [article] Force- and displacement-based seismic performance parameters for reinforced masonry structural walls with boundary elements [texte imprimé] / Bennett R. Banting, Auteur ; El-Dakhakhni, Wael W., Auteur . - 2013 . - pp. 1477–1491. Génie Civil Langues : Anglais (eng) in Journal of structural engineering > Vol. 138 N° 12 (Décembre 2012) . - pp. 1477–1491 Mots-clés : Cyclic  loads  Reinforced  masonry  Seismic  performance  Structural  walls  Wall  confinement Résumé : There is a need to evaluate existing, and introduce new, masonry construction techniques within a performance-based seismic design context to advance their adoption in the next generation of seismic design codes in North America. In this regard, a reinforced masonry (RM) structural wall system that incorporates confining boundary elements in the plastic hinge region presently lacks specific design requirements in the Masonry Standards Joint Committee and Canadian Standards Association S304.1 design codes. In addition, RM structural wall systems are omitted completely from the plan to develop a new performance-based seismic design methodology laid out by FEMA 445. This paper presents experimental results of four specially detailed RM structural walls subjected to fully reversed cycles of displacement-controlled loading as tested by the authors. In addition, the resulting analysis also includes one wall from a previous study for comparison purposes. All walls were detailed with lateral reinforcing ties confining a grouted core and four vertical reinforcement bars located at each of the wall ends. The design and detailing of the walls represented a range of parameters that would be anticipated to vary within low-to-medium-rise RM buildings. Each of the half-scale walls had overall dimensions of 1.8×4.0 m but varied by the level of applied axial load, the presence of interstory floor slabs, and the presence of confining boundary elements above the first-story height. The results of this experimental program indicate that boundary elements delayed the onset of buckling in the vertical reinforcement and reduced the impact of face-shell spalling on overall wall strength degradation. At 20% degradation from ultimate strength, the top drifts ranged from 1.82 to 3.73% and the displacement ductilities ranged from 6.6 to 15.2. This study is the first of a series of studies at McMaster University currently focused on introducing a broad set of experimental evidence aiming at establishing a new category of RM seismic force resisting systems in North American building codes. ISSN : 0733-9445 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29ST.1943-541X.0000572

Response of arching unreinforced concrete masonry walls to blast loading / Badr M. Abou-Zeid in Journal of structural engineering, Vol. 137 N° 10 (Octobre 2011) 

Public ISBD [article]  in Journal of structural engineering > Vol. 137 N° 10 (Octobre 2011) . - pp. 1205-1214 Titre : Response of arching unreinforced concrete masonry walls to blast loading Type de document : texte imprimé Auteurs : Badr M. Abou-Zeid, Auteur ; El-Dakhakhni, Wael W., Auteur ; A. Ghani Razaqpur, Auteur Année de publication : 2012 Article en page(s) : pp. 1205-1214 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Arching  action  Blast  loads  Concrete  masonry  Experimental  results  Out-of-plane  capacity  Retrofit  methods  System  identification Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : New standards for blast protection of buildings are currently being developed in the United States and Canada. In this regard, both standards are considering unreinforced masonry (URM) walls as particularly vulnerable to blast events and may not be used in blast-resisting structural systems. In this paper, the effectiveness of enforcing arching action as a cost-effective hardening technique for vertically spanning one-way URM walls under blast loads is investigated. A total of eight full-scale concrete-block URM walls were subjected to blast loads generated by high explosives. Enforcing URM walls arching between rigid supports significantly enhanced their out-of-plane blast resistance compared to similar nonarching (flexural) URM walls. Moreover, no fragments or debris were observed on the leeward side of the arching walls, indicating the potential of the proposed hardening technique in reducing the hazard level on the occupants of buildings with exterior URM walls. The improved performance is attributed to the formation of hinges at the walls’ supports and midheights. This three-hinged arch mechanism allowed the walls to develop large in-plane compressive forces, which subsequently increased their out-of-plane resistances and prevented flying debris due to increased friction forces between the masonry courses. Comparing the observed strength of the arched walls to their strength predicted by existing models showed a significant underestimation of the actual wall strengths. The results of the study clearly demonstrate that, with minimal structural intervention, URM walls can significantly improve the building envelope performance and contribute to the structural resistance of blast loads. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v137/i10/p1205_s1?isAuthorized=no [article] Response of arching unreinforced concrete masonry walls to blast loading [texte imprimé] / Badr M. Abou-Zeid, Auteur ; El-Dakhakhni, Wael W., Auteur ; A. Ghani Razaqpur, Auteur . - 2012 . - pp. 1205-1214. Génie Civil Langues : Anglais (eng) in Journal of structural engineering > Vol. 137 N° 10 (Octobre 2011) . - pp. 1205-1214 Mots-clés : Arching  action  Blast  loads  Concrete  masonry  Experimental  results  Out-of-plane  capacity  Retrofit  methods  System  identification Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : New standards for blast protection of buildings are currently being developed in the United States and Canada. In this regard, both standards are considering unreinforced masonry (URM) walls as particularly vulnerable to blast events and may not be used in blast-resisting structural systems. In this paper, the effectiveness of enforcing arching action as a cost-effective hardening technique for vertically spanning one-way URM walls under blast loads is investigated. A total of eight full-scale concrete-block URM walls were subjected to blast loads generated by high explosives. Enforcing URM walls arching between rigid supports significantly enhanced their out-of-plane blast resistance compared to similar nonarching (flexural) URM walls. Moreover, no fragments or debris were observed on the leeward side of the arching walls, indicating the potential of the proposed hardening technique in reducing the hazard level on the occupants of buildings with exterior URM walls. The improved performance is attributed to the formation of hinges at the walls’ supports and midheights. This three-hinged arch mechanism allowed the walls to develop large in-plane compressive forces, which subsequently increased their out-of-plane resistances and prevented flying debris due to increased friction forces between the masonry courses. Comparing the observed strength of the arched walls to their strength predicted by existing models showed a significant underestimation of the actual wall strengths. The results of the study clearly demonstrate that, with minimal structural intervention, URM walls can significantly improve the building envelope performance and contribute to the structural resistance of blast loads. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v137/i10/p1205_s1?isAuthorized=no