Download or read book Selection of a Material Model for Simulating Concrete Masonry Walls Subjected to Blast written by and published by . This book was released on 2004 with total page 147 pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the most common methods of construction is the use of concrete masonry units (CMU) in the walls of buildings. However, they are vulnerable to blast, and result in collapse, fragmentation, and severe injury to occupants. An understanding of the behavior of CMU walls during blast is key to developing mitigation techniques. Research has been conducted using the finite element method to simulate structural failure due to blast. A common problem faced by model developers is the selection of constitutive relationships that appropriately simulate the behavior of materials subjected to shock loading. This project examined the effect of blast impulse loading on CMU blocks. Finite element models were used to perform direct transient analysis using various material cards available in LS-DYNA, and the results were compared to the results of full-scale blast tests conducted by AFRL. The material card that best agreed with the test results was recommended for use in the models of polymer reinforced masonry walls.

Download or read book Collapse Analysis of Masonry Structures Under Earthquake Actions written by Tammam Bakeer and published by Tammam Bakeer. This book was released on 2009 with total page 266 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Advanced Computational Dynamics Simulation of Protective Structures Research written by and published by . This book was released on 2008 with total page 41 pages. Available in PDF, EPUB and Kindle. Book excerpt: Mitigation techniques are currently sought to ensure public safety in the event of intentional or accidental explosions. The use of concrete masonry walls in civilian and military buildings is one of the most common methods of construction. These walls, however, are vulnerable to impulse loads, and can result in collapse, fragmentation and severe injury to occupants. Over the past several years, the Airbase Technologies Division of the Air Force Research Laboratory has investigated methods of retrofitting concrete masonry walls to better resist blast loads from external explosions. One method that was demonstrated to be very effective is the application of thin membranes of high elongation materials to the inside surface of the walls. Due to the nonlinear behavior of concrete masonry walls, the use of advanced simulation techniques provides certain advantages over experiments for full understanding of their structural responses under explosive loads. In the present study, several finite element models were developed according to blast test conditions, and analyzed using LS-DYNA explicit code. Input sensitivity studies were conducted to investigate the variations of a wide range of parameters on wall deformation, damping coefficients, boundary conditions and arching action. The effort has led to cost effective analysis techniques for use by structural engineers in designing membrane retrofit concrete masonry walls subjected to blast loads. This report summarizes the simulation methodologies, challenges, techniques and comparison to full-scale dynamic tests for membrane retrofit concrete masonry walls.

Download or read book Development of Computational Models and Input Sensitivity Study of Polymer Reinforced Concrete Masonry Walls Subjected to Blast written by and published by . This book was released on 2004 with total page 170 pages. Available in PDF, EPUB and Kindle. Book excerpt: Computational models were developed and used to simulate polymer reinforced masonry walls subjected to blast loading and the models were used to understand the response of the structure. LS-DYNA, a nonlinear finite element solver, was used. Model development challenges were considered, and appropriate input parameters were determined. With these pedestal values, a baseline model of one unit width of concrete masonry block was developed, and the response under two load conditions was studied. Dimensional and mechanical variants involved in the system were varied to study their effect on wall behavior. The effects of door and window openings on the performance of the polymer reinforcement were evaluated. This report also presents an analysis of strain rate that occurs in the polymer coating and results were compared to theory-based closed form solutions. Finally, the static nonlinear capabilities of LS-DYNA were used to describe the static resistance of the system, and a theoretical description of a simply supported membrane subjected to pressure load is provided and compared with nonlinear finite element results.

Download or read book Structural Studies Repairs and Maintenance of Heritage Architecture X written by C. A. Brebbia and published by WIT Press. This book was released on 2007 with total page 737 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume contains papers presented at the Ninth International Conference on Structural Studies, Repairs and Maintenance of Heritage Architecture. The conference provides an ideal forum for professionals in the area to discuss problems and solutions, and exchange opinions and experiences.

Download or read book Concrete Masonry Wall Retrofit Systems for Blast Protection written by Carol Faye Johnson and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The increased threat against government and public facilities in the United States and abroad has highlighted the need to provide an economic and efficient method to retrofit existing conventional structures. Hollow, unreinforced, concrete masonry unit (CMU) infill walls, commonly used in reinforced concrete or steel framed structures, are particularly vulnerable to blast loads. Facilities that incorporate CMU walls must either be hardened or retrofitted for explosive events. Conventional retrofit techniques that focus on increasing the overall strength of the structure by adding steel or concrete are difficult to implement, time consuming, expensive, and in some cases, increase the debris hazard. The current research presents an alternative retrofit system for CMU walls that involves the application of an elastomeric material applied to the interior surface of the wall to prevent secondary debris in the form of CMU fragments from entering the structure when it is exposed to blast loads. The experimental program used to evaluate the alternative retrofit systems was divided into three phases. In Phase one, resistance functions for seven different retrofit systems were developed in 24 subscale static experiments. In Phase two, the structural response of the retrofit systems subjected to blast loads was evaluated in 25 subscale experiments. The final phase of the experimental program consisted of 18 full-scale high-explosive (HE) experiments used to validate the structural response observed in the subscale dynamic experiments. Data generated from the experimental program were used to develop a single-degree-of-freedom (SDOF) model to predict the mid-span deflection of the retrofitted CMU walls subjected to blast loads. The subscale resistance functions from Phase one were scaled and used in the SDOF model. The full-scale experimental results and the predicted results from the model were compared and the retrofit systems were ranked according to the qualitative and quantitative results obtained from the experimental and analytical research. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/151905

Download or read book Concrete Masonry Unit Walls Retrofitted with Elastomeric Systems for Blast Loads written by and published by . This book was released on 2004 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: Concrete masonry units (CMU), commonly referred to as concrete blocks, are the most common construction material utilized throughout the United States and the world for exterior walls of conventional structures. While masonry provides adequate strength for conventional design loads, it does not meet the minimum design standards mandated for blast protection of new and renovated government facilities. One of the most dangerous aspects of blast response is debris hazard, defined as high-velocity fragments originating from walls, windows, light fixtures, equipment, and furniture. Retrofits for conventional structures have evolved over the years from blast hardening through the addition of mass using concrete or steel, to the application of lighter, more resilient and ductile materials. Research at ERDC has focused on the use of elastomeric materials to mitigate debris hazards resulting from blast events. A series of sub-scale and full-scale experiments was conducted by ERDC to investigate the potential benefit of elastomeric retrofit systems when applied to hollow, unreinforced, CMU walls subjected to an explosive event. This study discusses both the 1/4-scale static and dynamic experiments and the full-scale dynamic CMU wall experiments conducted over the past few years. The CMU wall response to static loading was characterized by resistance functions, and normalized pressure and impulse diagrams were used to characterize the dynamic loading.

Download or read book Blast Simulator Wall Tests written by Michael G. Oesterle and published by . This book was released on 2009 with total page 655 pages. Available in PDF, EPUB and Kindle. Book excerpt: Loads generated in explosions that result from terrorist attacks and industrial accidents create devastating hazards for buildings and their occupants. The objective of this dissertation is to develop design guidelines and methodologies for protective/hardening strategies used to mitigate blast hazards in reinforced concrete and concrete masonry walls. Commonly, guidelines and methodologies are developed from experimental data. Field testing with live explosive is a reliable experimental method for demonstrating the performance of blast resistant concepts, but it is expensive, time consuming, and often produces low quality data. Static testing is another experimental method that allows researchers to clearly observe behavior and failure modes of structural components; however this too is limited because it cannot account for the rate effects associated with blast loads. The UCSD Blast Simulator was developed to offers an alternative method for testing structures to loads generated in an explosion without the difficulties and limitations associated with field and static testing. For this dissertation, tests were conducted with the blast simulator to study reinforced concrete walls protected with frangible panels, concrete masonry walls strengthened with carbon fiber reinforced polymer composite, and unreinforced masonry walls retrofitted with polyurea catcher systems. The objective of the dissertation was achieved through a succession of tasks that included; the development of a test protocol, validation and implementation of numerical models to predict loads delivered to specimens during blast simulator tests, development of method to correlate blast simulator loads to air blast loads, generation of high quality data on specimens with mitigation strategies for validation of numerical models to predict response of hardened/protected reinforced concrete and concrete masonry walls, and investigation of design variables with parametric studies. The investigation of concrete masonry walls demonstrated that the addition of carbon fiber reinforced polymers can increase the resistance to blast loads, but may result in a brittle failure mode. The study of reinforced concrete walls showed that frangible panels can improve the response by adding mass to the system. Finally, the research performed on unreinforced masonry walls with polyurea catcher emphasized the need for proper connection detailing.

Download or read book Nonlinear Analysis of Reinforced Concrete Masonry Walls Under Simulated Seismic Loadings written by Henriette Lebre La Rovere and published by . This book was released on 1990 with total page 408 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Blast Retrofit of Unreinforced Masonry Walls Using Fabric Reinforced Cementitious Matrix FRCM Composites written by Hyunchul Jung and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Unreinforced masonry (URM) walls are commonly found in existing and heritage buildings in Canada, either as infill or load-bearing walls. Such walls are vulnerable to sudden and brittle failure under blast loads due to their insufficient out-of-plane strength. The failure of such walls under blast pressures can also result in fragmentation and wall debris which can injure building occupants. Over the years, researchers have conducted experimental tests to evaluate the structural behaviour of unreinforced masonry walls under out-of-plane loading. Various strengthening methods have been proposed, including the use of concrete overlays, polyurea coatings and advanced fiber-reinforced polymer (FRP) composites. Fabric-reinforced cementitious matrix (FRCM) is an emerging material which can also be used to strengthen and remove the deficiencies in unreinforced masonry walls. This composite material consists of a sequence of one or multiple layers of cement-based mortar reinforced with an open mesh of dry fibers (fabric). This thesis presents an experimental and analytical study which investigates the effectiveness of using FRCM composites to improve the out-of-plane resistance of URM walls when subjected to blast loading. As part of the experimental program, two large-scale URM masonry walls were constructed and strengthened with the 3-plies of unidirectional carbon FRCM retrofit. The specimens included one infill concrete masonry (CMU) wall, and one load-bearing stone wall. The University of Ottawa Shock Tube was used to test the walls under gradually increasing blast pressures until failure, and the results were compared to those of control (un-retrofitted) walls tested in previous research. Overall, the FRCM strengthening method was found to be a promising retrofit technique to increase the blast resistance of unreinforced masonry walls. In particular, the retrofit was effective in increasing the out-of-plane strength, stiffness and ultimate blast capacity of the walls, while delaying brittle failure and reducing fragmentation. As part of the analytical research, Single Degree of Freedom (SDOF) analysis was performed to predict the blast behaviour of the stone load-bearing retrofit wall. This was done by computing wall flexural strength using Plane Section Analysis, and developing an idealized resistance curve for use in the SDOF analysis. Overall, the dynamic analysis results were found to be in reasonable agreement with the experimental maximum displacements.

Download or read book Resistance of Multi Wythe Insulted Masonry Walls Subjected to Impulse Loads written by and published by . This book was released on 2008 with total page 203 pages. Available in PDF, EPUB and Kindle. Book excerpt: The overall objective of this project was to define the dynamic flexural resistance of multi-wythe insulated masonry walls with specific emphasis placed on determining the potential application of foam insulation as a blast-resistant material. The project was closely coordinated with full-scale explosive testing conducted by personnel at the Airbase Technologies Division of the Air Force Research Laboratory (AFRL) at Tyndall Air Force Base Florida. The project involved the following tasks: (1) use of finite element (FE) and single-degree-of-freedom (SDOF) analytical models for test analysis and prediction of results, (2) identification of the constitutive relationships of insulating foam(s), (3) synthesis of full-scale test methodology and results, (4) utilization of the data gathered from the full-scale tests to validate the FE models, (5) implementation of input parameter studies using the advanced FE models to characterize the mechanical behavior of the systems tested, and (6) development of engineering-level resistance definitions and multi-degree-of-freedom models of multi-wythe insulated masonry walls. Four standard wall section designs were recommended by the National Concrete Masonry Association (NCMA). Of these designs, two were selected for full-scale testing: a conventional block wall with a brick veneer and an A-block wall with a brick veneer - both with extruded polystyrene board insulation in the cavity and cells fully grouted. A single-wythe control wall with equivalent mass and flexural capacity was also included in the tests. FE models were used to assess the ability of the insulation to reduce the peak deflection of masonry walls subjected to impulse loads. Observations regarding the crushing of the insulation during the full-scale testing are also presented.

Download or read book Performance of Polyurea Retrofitted Unreinforced Concrete Masonry Walls Under Blast Loading written by Laura Ciornei and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Unreinforced masonry walls subjected to blast loading are vulnerable to collapse and fragmentation. The objective of this thesis is to conduct experimental and analytical research for developing a blast retrofit methodology that utilizes polyurea. A total of four unreinforced masonry walls were constructed and tested under various shock tube induced blast pressures at the University of Ottawa Shock Tube Testing Facility. Two of the retrofitted walls had surface-sprayed polyurea. The results indicate that the use of polyurea effectively controlled fragmentation while significantly increased the load capacity and stiffness of masonry walls. Polyurea proved to be an excellent retrofit material for dissipating blast induced energy by providing ductility to the system and changing the failure mode from brittle to ductile. Single degree of freedom (SDOF) dynamic analyses were conducted as part of the analytical investigation. The results show that the analytical model provides reasonably accurate predictions of the specimen response.

Download or read book Post tensioned Concrete Masonry Walls Subjected to Uniform Lateral Loading written by Gabriel Gadison Aridru and published by . This book was released on 1992 with total page 200 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Advances in Protective Structures Research written by Hong Hao and published by CRC Press. This book was released on 2012-08-17 with total page 409 pages. Available in PDF, EPUB and Kindle. Book excerpt: The International Association of Protective Structures (IAPS) was launched on 1 October 2010 in Manchester, UK during the first International Conference of Protective Structures. The primary purpose of IAPS is to bring researchers and engineers working in the area of protective structures together, and to promote research and development work for b

Download or read book Mechanics of Masonry Structures written by Maurizio Angelillo and published by Springer Science & Business Media. This book was released on 2014-03-20 with total page 350 pages. Available in PDF, EPUB and Kindle. Book excerpt: The experience of people working with different perspectives in different fields of masonry modeling, from mathematics to applied engineering and practice, is brought together in this book. It presents both the theoretical background and an overview of the state-of-the-art in static and dynamic masonry modeling.

Download or read book Structures Under Shock and Impact X written by Norman Jones and published by WIT Press. This book was released on 2008 with total page 417 pages. Available in PDF, EPUB and Kindle. Book excerpt: This text examines the interaction between blast pressure and surface or underground structures, whether the blast is from civilian, military, dust and natural explosions, or any other source.

Download or read book Blast Retrofit of Unreinforced Masonry Walls Using ECC Shotcrete written by Jordan Gandia and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Blast loads on buildings can originate from accidental explosions or from targeted attacks. Design against blast loads has become an increasingly important topic due to the current political climate. Unfortunately, many older buildings are constructed with unreinforced masonry (URM) walls which are particularly susceptible to out of plane failures caused by blast loads. One solution to increase the safety of these buildings is to retrofit them with advanced materials that can increase their out-of-plane stiffness and resistance. This thesis investigates the potential of using a high-performance shotcrete as a retrofit system for URM walls against blast effects. The shotcrete used in this study is made from Engineered Cementitious Composite (ECC), a special type of fiber-reinforced cementitious material, with high ductility and high energy-absorption capacity. The ECC shotcrete replaces aggregates with synthetic microfibers to increase tensile strength and ductility. A welded wire mesh was embedded in the shotcrete to provide ductile behavior. The testing program includes a total of six large-scale unreinforced masonry wall specimens. Two walls were constructed using concrete masonry unit (CMU) blocks to be retrofitted. The first specimen was built as an infill wall, experiencing no axial load, while the second specimen was built as a load bearing wall, with 10% axial load. Four more walls were built out of stone blocks. Two of the stone walls were controls: one infill and one load bearing (4% axial load). The other two stone walls were retrofit with the shotcrete system: one infill and one load bearing (4% axial load). The blast loads were simulated using the University of Ottawa's Shock Tube. The walls were restrained at the top and bottom with a shear restraint to induce one way bending. Pressure, displacement and strain data were acquired with the use of pressure gauges, LVDT's, strain gauges and cameras. The specimens were subjected to gradually increasing blast pressures until failure. The performance of the specimens was observed by analyzing the displacement, crack widths, fragmentation and failure mode. The results indicate the benefits of using ECC shotcrete as a retrofit system. The displacements of the retrofit walls were very small compared to the control walls, and fragments were limited. The specimens with axial load were found to have increased resistance. While the failure mode was brittle for the retrofit walls, this can be avoided with the use of a mesh with a larger area of steel. A SDOF analysis was performed to predict the blast response of the test walls. The analysis was done by generating resistance functions for the walls through analytical models. The analysis was found to agree reasonably well with the experimental data.