Stress-Crack Separation Relationship for Macrosynthetic, Steel and Hybrid Fiber Reinforced Concrete

An experimental evaluation of the crack propaga tion and post-cracking response of macro fiber reinforced concrete in flexure is c onducted. Two types of structur al fibers, hooked end steel fibers and continuousl y embossed macro-synthetic fibers are used in this study. A fiber blend of the two fibers is evaluated for spec ific improvements in the post peak residual load carrying response. At 0.5% volume fraction, both steel and macrosynthetic fiber reinforced concrete exhibits load recovery at large crack opening. The blend of 0.2% macrosynthetic fibers and 0.3% steel fibers shows a significa nt improvement in the immediate post peak load response with a significantly smaller load drop and a constant residual load carrying capacity equal to 80% of the peak load. An analytical formulation to predict fle xure load-displacement behaviour considering a multi-linear stress- crack separation (σ -w) relationship is developed. An inverse analysis is developed for obtaining the multi- linear σ -w relation, from the experimental response. The � -w curves of the steel and macrosynthetic fiber reinforced concrete exhibit a stress recovery after a significant drop with increa sing crack opening. Significant residual load carrying capacity is attained only at large crack separation. The fiber blend exhibits a constant residual stress with increasing crack sepa ration following an initial decrease. The constant residual stress is attained at a small crack separation

A new mixed model based on the enhanced-Refined Zigzag Theory for the analysis of thick multilayered composite plates

The Refined Zigzag Theory (RZT) has been widely used in the numerical analysis of multilayered and sandwich plates in the last decay. It has been demonstrated its high accuracy in predicting global quantities, such as maximum displacement, frequencies and buckling loads, and local quantities such as through-the-thickness distribution of displacements and in-plane stresses [1,2]. Moreover, the C0 continuity conditions make this theory appealing to finite element formulations [3]. The standard RZT, due to the derivation of the zigzag functions, cannot be used to investigate the structural behaviour of angle-ply laminated plates. This drawback has been recently solved by introducing a new set of generalized zigzag functions that allow the coupling effect between the local contribution of the zigzag displacements [4]. The newly developed theory has been named enhanced Refined Zigzag Theory (en- RZT) and has been demonstrated to be very accurate in the prediction of displacements, frequencies, buckling loads and stresses. The predictive capabilities of standard RZT for transverse shear stress distributions can be improved using the Reissner’s Mixed Variational Theorem (RMVT). In the mixed RZT, named RZT(m) [5], the assumed transverse shear stresses are derived from the integration of local three-dimensional equilibrium equations. Following the variational statement described by Auricchio and Sacco [6], the purpose of this work is to implement a mixed variational formulation for the en-RZT, in order to improve the accuracy of the predicted transverse stress distributions. The assumed kinematic field is cubic for the in-plane displacements and parabolic for the transverse one. Using an appropriate procedure enforcing the transverse shear stresses null on both the top and bottom surface, a new set of enhanced piecewise cubic zigzag functions are obtained. The transverse normal stress is assumed as a smeared cubic function along the laminate thickness. The assumed transverse shear stresses profile is derived from the integration of local three-dimensional equilibrium equations. The variational functional is the sum of three contributions: (1) one related to the membrane-bending deformation with a full displacement formulation, (2) the Hellinger-Reissner functional for the transverse normal and shear terms and (3) a penalty functional adopted to enforce the compatibility between the strains coming from the displacement field and new “strain” independent variables. The entire formulation is developed and the governing equations are derived for cases with existing analytical solutions. Finally, to assess the proposed model’s predictive capabilities, results are compared with an exact three-dimensional solution, when available, or high-fidelity finite elements 3D models. References: [1] Tessler A, Di Sciuva M, Gherlone M. Refined Zigzag Theory for Laminated Composite and Sandwich Plates. NASA/TP- 2009-215561 2009:1–53. [2] Iurlaro L, Gherlone M, Di Sciuva M, Tessler A. Assessment of the Refined Zigzag Theory for bending, vibration, and buckling of sandwich plates: a comparative study of different theories. Composite Structures 2013;106:777–92. https://doi.org/10.1016/j.compstruct.2013.07.019. [3] Di Sciuva M, Gherlone M, Iurlaro L, Tessler A. A class of higher-order C0 composite and sandwich beam elements based on the Refined Zigzag Theory. Composite Structures 2015;132:784–803. https://doi.org/10.1016/j.compstruct.2015.06.071. [4] Sorrenti M, Di Sciuva M. An enhancement of the warping shear functions of Refined Zigzag Theory. Journal of Applied Mechanics 2021;88:7. https://doi.org/10.1115/1.4050908. [5] Iurlaro L, Gherlone M, Di Sciuva M, Tessler A. A Multi-scale Refined Zigzag Theory for Multilayered Composite and Sandwich Plates with Improved Transverse Shear Stresses, Ibiza, Spain: 2013. [6] Auricchio F, Sacco E. Refined First-Order Shear Deformation Theory Models for Composite Laminates. J Appl Mech 2003;70:381–90. https://doi.org/10.1115/1.1572901

Behavior of Hybrid NSM Reinforced and Externally Confined Reinforced Concrete Columns under Eccentric Compression –Experimental and Numerical Studies

The effectiveness of hybrid combination of ne ar surface mounted (NSM) and externally confined (EC) FRP strengthenin g on the performance of RC column elements under uniaxial eccentric compression is investigated. In total, ten short RC column elements were cast. Carbon FRP is used for strengthening due to its inherent stiffness and strength properties on par with other FRP materials. The columns were strengthened using NSM CFRP laminates, EC using CFRP fabrics and their hybrid combi nations. A non-linear finite element model is developed using ABAQUS and the numerical model is calibrated using the experimental results to improve the accuracy of the predict ions. Experimental results revealed that hybrid strengthening of RC columns was able to show a better performance in terms of stiffness, strength, ultimate displacement ductility when compared to other FRP strengthening techniques. The numerical predictions obtained were able to better capture the initial stiffness, peak load and post-peak behavior. Thus, the proposed hybrid strengthening technique for RC columns possess the capability of restoring the loss in stiffness, strength and ductility due to additional bending moment induced by the eccentric compression loading

Role of Steel Fibers in Shear Resistance of Beams in Arch Action

Reinforced concrete beams with discrete hooked-end steel fibe rs were tested with a shear span to depth ratio equal to 1.8. Digital im age correlation (DIC) technique was used to obtain the full-field displacements from the beam during the load response. The formation and propagation of a shear crack which directly influences the load response and peak load in the load response of the beam is moni tored using the displacement fr om the DIC measurements. There is a continuous slip across the crack face s of the shear crack with increasing load carrying capacity up to the peak load. The shear crack exhibits a dilatant behavior with increasing slip. Failure in control beams is brittle which was by the opening of dominant shear crack in shear span at a small value of crack opening. At the peak load, the shear crack pattern in fiber reinforced conc rete was identical to the crack pattern in the control beam. The dilatant behavior from the measured crack opening a nd crack slip displacements obtained from the control and the SFRC beams is identical. The fiber reinforced concrete beams exhibit a ductile response with a post peak load car rying capacity even after the continued opening of the dominant shear crack

Role of Reactive Alumina and Reactive Oxide Ratios on Strength Development in Alakaline Activation of Low-Calcium Fly Ash

The role of reactive alumina and process varia bles such as sodium content and molarity on alkaline activation of different low calcium fly ashes are explored. Reactive alumina content of a fly ash is the key parameter which dete rmines the maximum compressive strength achieved from the alkaline activati on. The oxide ratios in the activated system, based on the total silica in the system consisting of the re active silica contributed by fly ash and the reactive alumina in fly ash are shown to provide consistent results for achieving the highest strength. A method called XRD-based direct decomposition is used to determine the unreacted glassy content and amorphous reaction product in the system. The strength gain in the system is directly related to a decrease in the unreacted fly ash glassy content and an increase in the reaction product content in the system

International Conference on Civil Infrastructure and Construction (CIC 2020)

This is the proceedings of the CIC 2020 Conference, which was held under the patronage of His Excellency Sheikh Khalid bin Khalifa bin Abdulaziz Al Thani in Doha, Qatar from 2 to 5 February 2020. The goal of the conference was to provide a platform to discuss next-generation infrastructure and its construction among key players such as researchers, industry professionals and leaders, local government agencies, clients, construction contractors and policymakers. The conference gathered industry and academia to disseminate their research and field experiences in multiple areas of civil engineering. It was also a unique opportunity for companies and organizations to show the most recent advances in the field of civil infrastructure and construction. The conference covered a wide range of timely topics that address the needs of the construction industry all over the world and particularly in Qatar. All papers were peer reviewed by experts in their field and edited for publication. The conference accepted a total number of 127 papers submitted by authors from five different continents under the following four themes: Theme 1: Construction Management and Process Theme 2: Materials and Transportation Engineering Theme 3: Geotechnical, Environmental, and Geo-environmental Engineering Theme 4: Sustainability, Renovation, and Monitoring of Civil InfrastructureThe list of the Sponsors are listed at page 1

Novel Approaches for Structural Health Monitoring

The thirty-plus years of progress in the field of structural health monitoring (SHM) have left a paramount impact on our everyday lives. Be it for the monitoring of fixed- and rotary-wing aircrafts, for the preservation of the cultural and architectural heritage, or for the predictive maintenance of long-span bridges or wind farms, SHM has shaped the framework of many engineering fields. Given the current state of quantitative and principled methodologies, it is nowadays possible to rapidly and consistently evaluate the structural safety of industrial machines, modern concrete buildings, historical masonry complexes, etc., to test their capability and to serve their intended purpose. However, old unsolved problematics as well as new challenges exist. Furthermore, unprecedented conditions, such as stricter safety requirements and ageing civil infrastructure, pose new challenges for confrontation. Therefore, this Special Issue gathers the main contributions of academics and practitioners in civil, aerospace, and mechanical engineering to provide a common ground for structural health monitoring in dealing with old and new aspects of this ever-growing research field

Development of BIM-based Automated Methods for Building Management and Structural Safety Assessment

Despite the progress made in modern project management methods, there is still a lack of appropriate automated tools that support digital integration over the project life cycle. There is considerable demand for fully embracing the latest technological opportunities such as Building Information Modeling (BIM), Internet of Things (IoT), Structural Health Monitoring (SHM), and prefabrication to support that digital transformation in construction. The aim of this study is to develop a set of automated management solutions and related tools to address the issues highlighted above. The thesis is presented as a collection of manuscripts of five peer-reviewed journal articles authored based on the present research. The first development is of a BIM-based method for 3D model visualization of buildings and their non-structural elements and their corresponding seismic risk levels and locations. It supports automated assessment of seismic risk of these elements. The second focuses on the development of a novel data-driven SHM technique to monitor the structural behavior of individual building modules to detect possible damages during their transportation. It consists of two main components, a sensor-based data acquisition (DAQ) and storage module, and an automated data analysis module that uses unsupervised machine learning techniques to identify damages during transportation using onboard captured acceleration data. It can be used to ascertain the safety of delivered modules before their assembly on site. The third accounts for the development of an automated BIM-based framework to facilitate effective data management and representation of sensory components of the SHM tool used in buildings. It allows for visualization of damages in building components based on the interpretation of the captured sensor data. It is designed to facilitate effective visualization capabilities for a rapid and efficient structural condition assessment. The fourth development is designed to dynamically update the thermal comfort data in monitored buildings by integrating their BIM models with captured sensor data. The default range utilized in this development is based on the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Standard. It is expected to provide a robust and practical tool for data collection, analysis, and visualization to facilitate intelligent monitoring of the thermal condition in buildings and help decision-makers take needed timely data-driven decisions. The fifth and last development is designed to alert IoT companies of malfunctioning of deployed sensors utilizing a BIM platform and a cloud database to process and transfer related actionable information

An EMI-Based Clustering for Structural Health Monitoring of NSM FRP Strengthening Systems

The use of fiber-reinforced polymers (FRP) in civil construction applications with the near-surface mounted (NSM) method has gained considerable popularity worldwide and can produce confident strengthening and repairing systems for existing concrete structures. By using this technique, the FRP reinforcement is installed into slits cut into the concrete cover using cement mortar or epoxy as bonding materials, yielding an attractive method to strengthen concrete structures as an advantageous alternative to the external bonding of FRP sheets. However, in addition to the two conventional failure modes of concrete beams, sudden and brittle debonding failures are still likely to happen. Due to this, a damage identification technology able to identify anomalies at early stages is needed. In this work, some relevant cluster-based methods and their adaptation to electromechanical impedance (EMI)-based damage detection in NSM-FRP strengthened structures are developed and validated with experimental tests. The performance of the proposed clustering approaches and their evaluation in comparison with the experimental observations have shown a strong potential of these techniques as damage identification methodology in an especially complex problem such as NSM-FRP strengthened concrete structures