Blast Retrofit of Unreinforced Masonry Walls Using Fabric Reinforced Cementitious Matrix (FRCM) Composites
Blast Retrofit of Unreinforced Masonry Walls Using Fabric Reinforced Cementitious Matrix (FRCM) Composites

Author: Hyunchul Jung

Publisher:

Published: 2020

Total Pages:

ISBN-13:

DOWNLOAD EBOOK

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.

Increasing the Blast Resistance of Concrete Masonry Walls Using Fabric Reinforced Cementitious Matrix (FRCM) Composites
Increasing the Blast Resistance of Concrete Masonry Walls Using Fabric Reinforced Cementitious Matrix (FRCM) Composites

Author: Ramon Perez Garcia

Publisher:

Published: 2021

Total Pages:

ISBN-13:

DOWNLOAD EBOOK

Unreinforced masonry (URM) walls are often used as load-bearing or infill walls in buildings in many countries. Such walls are also commonly found in existing and heritage buildings in Canada. URM walls are strong structural elements when subjected to axial loading, but are very vulnerable under out-of-plane loads. This type of loading may come from different sources , including seismic or blast events. When subjected to blast, wall elements experience large pressures on one of their faces due to the high pressure produced in the air when an explosion takes place. This wave of compressed air travels in a very short time and hits the wall causing immense stresses, which result in large shear and bending demands that may lead to wall failure, and the projection of debris at high velocities that can injure building occupants. This failure process is highly brittle due to the very low out-of-plane strength that characterize such walls. In the past years, many investigations have been carried out to enhance the structural behaviour of unreinforced masonry walls under out-of-plane loading. Different strengthening methods have been studied, which include the use of polyurea coatings, the application of advanced fiber-reinforced polymer (FRP) composites or the use of concrete overlays in combination with high performance reinforcement. Fabric-reinforced cementitious matrix (FRCM) is a new composite material that overcomes some of the drawbacks of FRP. This composite material consists of applying coatings which consist of one or more layers of cement-based mortar reinforced with a corresponding open mesh of dry fibers (fabric). This material has been studied as a strengthening technique to improve in-plane and out-of-plane capacity of existing URM walls as well as other structural elements, mostly under seismic actions. 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, three large-scale URM masonry walls were constructed and strengthened with 1,2 and 3 layers of FRCM using unidirectional carbon fabrics. In all cases the specimens were built as load-bearing concrete masonry (CMU) walls. To increase shear resistance, two of the walls were also grouted with a flowable self-compacting concrete (SCC) mortar. Blast tests were conducted using the University of Ottawa Shock Tube and the results are compared with control walls tested in previous research at the University of Ottawa. The experimental results show that the FRCM retrofit significantly improved the blast performance of the URM load-bearing walls, allowing for increased blast capacity and improved control of displacements. The performance of the retrofit was found to be dependent on the number of retrofit layers. As part of the analytical research, Single Degree of Freedom (SDOF) analysis was carried out to predict the blast behaviour of the strengthened walls. This was done by computing wall flexural strength using plane sectional analysis and developing idealized resistance curves for use in the SDOF analysis. In general, the analysis procedure is found to produce reasonably accurate results for both the resistance functions and wall mid-height displacements under blast loading.

Handbook for Blast Resistant Design of Buildings
Handbook for Blast Resistant Design of Buildings

Author: Donald O. Dusenberry

Publisher: John Wiley & Sons

Published: 2010-01-26

Total Pages: 513

ISBN-13: 0470170549

DOWNLOAD EBOOK

Unique single reference supports functional and cost-efficient designs of blast resistant buildings Now there's a single reference to which architects, designers, and engineers can turn for guidance on all the key elements of the design of blast resistant buildings that satisfy the new ASCE Standard for Blast Protection of Buildings as well as other ASCE, ACI, and AISC codes. The Handbook for Blast Resistant Design of Buildings features contributions from some of the most knowledgeable and experienced consultants and researchers in blast resistant design. This handbook is organized into four parts: Part 1, Design Considerations, sets forth basic principles, examining general considerations in the design process; risk analysis and reduction; criteria for acceptable performance; materials performance under the extraordinary blast environment; and performance verification for technologies and solution methodologies. Part 2, Blast Phenomena and Loading, describes the explosion environment, loading functions needed for blast response analysis, and fragmentation and associated methods for effects analysis. Part 3, System Analysis and Design, explains the analysis and design considerations for structural, building envelope, component space, site perimeter, and building system designs. Part 4, Blast Resistant Detailing, addresses the use of concrete, steel, and masonry in new designs as well as retrofitting existing structures. As the demand for blast resistant buildings continues to grow, readers can turn to the Handbook for Blast Resistant Design of Buildings, a unique single source of information, to support competent, functional, and cost-efficient designs.

Blast Simulator Wall Tests
Blast Simulator Wall Tests

Author: Michael G. Oesterle

Publisher:

Published: 2009

Total Pages: 655

ISBN-13:

DOWNLOAD EBOOK

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.

Blast Protection of Civil Infrastructures and Vehicles Using Composites
Blast Protection of Civil Infrastructures and Vehicles Using Composites

Author: Nasim Uddin

Publisher: Elsevier

Published: 2010-03-12

Total Pages: 448

ISBN-13: 1845698037

DOWNLOAD EBOOK

With the upsurge in terrorism in recent years and the possibility of accidental blast threats, there is growing interest in manufacturing blast ‘hardened’ structures and retrofitting blast mitigation materials to existing structures. Composites provide the ideal material for blast protection as they can be engineered to give different levels of protection by varying the reinforcements and matrices. Part one discusses general technical issues with chapters on topics such as blast threats and types of blast damage, processing polymer matrix composites for blast protection, standards and specifications for composite blast protection materials, high energy absorbing composite materials for blast resistant design, modelling the blast response of hybrid laminated composite plates and the response of composite panels to blast wave pressure loadings. Part two reviews applications including ceramic matrix composites for ballistic protection of vehicles and personnel, using composites to protect military vehicles from mine blasts, blast protection of buildings using FRP matrix composites, using composites in blast resistant walls for offshore, naval and defence related structures, using composites to improve the blast resistance of columns in buildings, retrofitting using fibre reinforced polymer composites for blast protection of buildings and retrofitting to improve the blast response of concrete masonry walls. With its distinguished editor and team of expert contributors, Blast protection of civil infrastructures and vehicles using composites is a standard reference for all those concerned with protecting structures from the effects of blasts in both the civil and military sectors. Reviews the role of composites in blast protection with an examination of technical issues, applications of composites and ceramic matrix composites Presents numerical examples of simplified blast load computation and an overview of the basics of high explosives includes important properties and physical forms Varying applications of composites for protection are explored including military and non-military vehicles and increased resistance in building columns and masonry walls

Blast Design of Reinforced Concrete and Masonry Components Retrofitted with FRP.
Blast Design of Reinforced Concrete and Masonry Components Retrofitted with FRP.

Author:

Publisher:

Published: 2010

Total Pages: 42

ISBN-13:

DOWNLOAD EBOOK

Fiber-reinforced polymer (FRP) products are used as an alternative to traditional methods for strengthening and retrofitting concrete and masonry structures to resist blast loads. The development and experimental validation of a methodology for modeling the response of blast loaded concrete and masonry structural components retrofitted with FRP, as well as corresponding response criteria, is important since these types of components often require upgrades in order to provide personnel protection in blast-loaded buildings. This paper discusses the development of a SDOF-based procedure for designing FRP upgrades to blast loaded masonry and concrete walls by Protection Engineering Consultants for the U.S. Army Corps of Engineers, Protective Design Center. This includes the methodology used to determine the flexural stiffness and ultimate flexural and shear resistance of the upgraded walls. The methodology for estimating the flexural resistance of concrete and masonry components is based on current codes and guidelines (ACI-318 and ACI 440.2R). Experimental data from previous shock tube tests on concrete and masonry walls retrofitted with FRP were used to validate the upgrade design procedure by comparing the observed and calculated response of the tested components. Furthermore, proposed response criteria were developed for flexural and shear response of the walls for damage levels used for DoD antiterrorism design. These damage levels can be correlated to those used in UFC 3-340-02 for explosive safety.

Blast Retrofit of Unreinforced Masonry Walls Using ECC Shotcrete
Blast Retrofit of Unreinforced Masonry Walls Using ECC Shotcrete

Author: Jordan Gandia

Publisher:

Published: 2019

Total Pages:

ISBN-13:

DOWNLOAD EBOOK

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.