International Science Index

International Journal of Structural and Construction Engineering

Computational Modeling of Perpendicular to Grain Stress in a Non-Standard Glulam Beam
This paper focuses on the analysis of tensile stresses perpendicular to the grain in simply supported beams with different geometry made of glued laminated timber. Two types of beams are considered: standard double-tapered beams described in Eurocode 5 and non-standard glulam beams with a flattened apex. The beams are analyzed using two methodology approaches: a code design verification method and a finite element method (FEM) in terms of the linear theory of elasticity with plane stress assumption. The performed analyses proved that both methodologies lead to consistent results in case of standard glulam beams and therefore, the FEM can be used in case of non-standard structures, which are not included in Eurocode 5. Moreover, the FE analysis of the glulam beam with a flattened apex showed that it can be treated as a structure with two apex zones.
Cable Supported Facades under Blast Loading
Structural Glass Facades (SGFs) are used in most modern buildings due to their unique architectural aesthetics and energy performance. Cable Supported Facades (CSFs), both cable truss facades and cable net facades are gaining in popularity among the SGFs due to their increased transparency and minimal and highly flexible supporting structures. With the increased threat of terrorist attacks around the world, designers are concerned in making these facades blast resistant for credible blast events as impact of flying glass fragments has been the primary cause of injury during a blast event. Early approaches to designing blast resistant facades identified Laminated Glass (LG) panels as the preferred glass type due to their high energy absorption capacity and the specific interlayer properties. Several design standards were developed for blast resistant design. However, these standards are conservative and less applicable to today’s innovative structural glass façade systems. There has been some recent research on developing methods to design CSFs subjected to blast events. However, most of these studies suggested the use of external devices to mitigate the adverse effects of a blast event on the façade. These developed systems have limitations in application and installation of external devices significantly increases the cost of the façade and the difficulty in construction. There is hence a need to develop a practical CSF system with a blast resisting capacity under credible blast loads. With this in mind, a research project has been undertaken to develop a CSF system without installing any expensive external devices, instead varying the system parameters to create a cost effective and efficient system for a credible blast event. The applications of systems and technology used in innovative wind resisting CSFs are considered for blast applications. Towards this end, this paper investigates the behavior of CSFs under blast loading by a numerical analyses carried out with the finite element models developed using LS DYNA simulation software. Modular units of cable net facades are created in FE code and modelling techniques are validated with existing numerical and experimental data. The behavior of facade elements under a pressure acting on the front face due to unconfined surface burst is evaluated. The material models, element formulations and connections and contact types for the different components of the cable supported façade are confirmed in an iterative manner by investigating different combinations. Finally, a comprehensive numerical model that can be used to analyze the global behavior of a CSF under credible blast pressure is proposed. This model can be used to study the influence of the controlling parameters and thereby to develop an optimized blast resistant CSF.
Response of Solar Updraft Power Plants Incorporating Material Nonlinearity
Solar updraft power plants (SUPP) provide a great potential for green and environmentally friendly renewable power generation. An up to 1000 m high chimney represents one of the major parts of each SUPP, which consist of the main shell structure and the stiffening rings. Including the nonlinear material behavior in a simulation of the chimney is computationally a demanding task. However, allowing the formation of cracking in concrete leads to a more economical design of the structure. In this work, an FE model of a SUPP is presented incorporating the nonlinear material behavior. The effect of wind loading intensity on the structural response is explored. Furthermore, the influence of the stiffness of the ring beams on the global behavior is as well investigated. The obtained results indicate that the minimum reinforcement is capable of carrying the tensile stresses provided that the ring beams are rather stiff.
Submodeling of Mega-Shell Reinforced Concrete Solar Chimneys
Solar updraft power plants (SUPPs) made from reinforced concrete (RC) are an innovative technology to generate solar electricity. An up to 1000 m high chimney represents the major part of each SUPP ensuring the updraft of the warmed air from the ground. Numerical simulation of nonlinear behavior of such large mega shell concrete structures is a challenging task, and computationally expensive. A general finite element approach to simulate reinforced concrete bearing behavior is presented and verified on a simply supported beam, as well as the technique of submodeling. The verified numerical approach is extended and consecutively transferred to a more complex chimney structure of a SUPP. The obtained results proved the reliability of submodeling technique in analyzing critical regions of simple and complex mega concrete structures with high accuracy and dramatic decrease in the computation time.
Analysis of Beams with Web Opening Subject to Vertical Loads
The steel beams with web opening including the cellular and castellated I-beams are fabricated from a solid web I-beam through a double cutting method to a specific shape and size along the beam. The two halves of the beams are then welded together, increasing the overall depth of the web section. In this paper, the deflection of the cellular and castellated beams subject to uniform vertical loads are investigated using Finite Element Autodesk simulation package. The structural response of the beams with web opening are compared with regular solid beams. Additionally, parametric studies are carried out to study the influence of the geometric properties of a cellular beam to its structural responses.
Modelling of Factors Affecting Bond Strength of Fibre Reinforced Polymers Externally Bonded to Timber and Concrete
In recent years, fibre reinforced polymers as applications of strengthening materials have received significant attention by civil engineers and environmentalists because of their excellent characteristics. Currently, these composites have become a mainstream technology for strengthening of infrastructures such as steel, concrete and more recently, timber and masonry structures. However, debonding is identified as the main problem which limits the full utilisation of the FRP material. In this paper, a preliminary analysis of factors affecting bond strength of FRP-to-concrete and timber bonded interface has been conducted. A novel theoretical method through regression analysis has been established to evaluate these factors. Results of proposed model are then assessed with results of pull-out tests, and satisfactory comparisons are achieved when measured failure loads compared against of predicted loads.
Finite Element Analysis of Steel-Concrete Composite Structures considering Bond-Slip Effect
A numerical model considering slip behavior of steel-concrete composite structure is introduced. This model is based on a linear bond stress-slip relation along the interface. Single node was considered at the interface of steel and concrete member in finite element analysis, and it improves analytical problems of model that takes double nodes at the interface by adopting spring elements to simulate the partial interaction. The slip behavior is simulated by modifying material properties of steel element contacting concrete according to the derived formulation. Decreased elastic modulus simulates the slip occurrence at the interface and decreased yield strength simulates drop in load capacity of the structure. The model is verified by comparing numerical analysis applying this model with experimental studies. Acknowledgment—This research was supported by a grant(13SCIPA01) from Smart Civil Infrastructure Research Program funded by Ministry of Land, Infrastructure and Transport(MOLIT) of Korea government and Korea Agency for Infrastructure Technology Advancement(KAIA) and financially supported by Korea Ministry of Land, Infrastructure and Transport(MOLIT) as U-City Master and Doctor Course Grant Program.
Quantification of Factors Contributing to Wave-in-Deck on Fixed Jacket Platforms
Wave-in-deck phenomenon for fixed jacket platforms at shallow water condition has been reported as a notable risk to the workability and reliability of the platform. Reduction in reservoir pressure, due to the extraction of hydrocarbon for an extended period of time, has caused the occurrence of seabed subsidence. Platform experiencing subsidence promotes reduction of air gaps, which eventually allows the waves to attack the bottom decks. The impact of the wave-in-deck generates additional loads to the structure and therefore increases the values of the moment arms. Higher moment arms trigger instability in terms of overturning, eventually decreases the reserve strength ratio (RSR) values of the structure. The mechanics of wave-in-decks, however, is still not well understood and have not been fully incorporated into the design codes and standards. Hence, it is necessary to revisit the current design codes and standards for platform design optimization. The aim of this study is to evaluate the effects of RSR due to wave-in-deck on four-legged jacket platforms in Malaysia. Base shear values with regards to calibration and modifications of wave characteristics were obtained using SESAM GeniE. Correspondingly, pushover analysis is conducted using USFOS to retrieve the RSR. The effects of the contributing factors i.e. the wave height, wave period and water depth with regards to the RSR and base shear values were analyzed and discussed. This research proposal is important in optimizing the design life of the existing and aging offshore structures. Outcomes of this research are expected to provide a proper evaluation of the wave-in-deck mechanics and in return contribute to the current mitigation strategies in managing the issue.
Performance Evaluation of Composite Beam under Uniform Corrosion
Composite member (concrete and steel) has been widely advanced for structural utilization due to its best performance in resisting load, reducing the total weight of the structure, increasing stiffness, and other available advantages. On the other hand, the environment load such as corrosion (e.g. chloride ingress) creates significant time-dependent degradation for steel. Analysis performed in this paper is mainly considered uniform corrosion for evaluating the composite beam without examining the pit corrosion as the initial corrosion formed. Corrosion level in terms of weight loss is modified in yield stress and modulus elasticity of steel. Those two mechanical properties are utilized in this paper for observing the stresses due to corrosion attacked. As corrosion level increases, the effective width of the composite beam in the concrete section will be wider. The position of a neutral axis of composite section will indicate the composite action due to corrosion of composite beam so that numerous shear connectors provided must be reconsidered. Flexure capacity quantification provides stresses, and shear capacity calculation derives connectors needed in overcoming the shear problem for composite beam under corrosion. A model of simply supported composite beam examined in this paper under uniform corrosion where the stresses as the focus of the evaluation. Principal stress at the first stage of composite construction decline as the corrosion level incline, parallel for the second stage stress analysis where the tension region held by the steel undergoes lower capacity due to corrosion. Total stresses of the composite section for steel to be born significantly decreases particularly in the outermost fiber of tension side. Whereas, the available compression side is smaller as the corrosion level increases so that the stress occurs on the compression side shows reduction as well. As a conclusion, the increment of corrosion level will degrade both compression and tension side of stresses.
Seismic Assessment of Flat Slab and Conventional Slab System for Irregular Building Equipped with Shear Wall
Particular instability of structural building under lateral load (e.g earthquake) will rise due to irregularity in vertical and horizontal direction as stated in SNI 03-1762-2012. The conventional slab has been considered for its less contribution in increasing the stability of the structure, except special slab system such as flat slab turned into account. In this paper, the analysis of flat slab system at Sequis Tower located in South Jakarta will be assessed its performance under earthquake. It consists of 6 floors of the basement where the flat slab system is applied. The flat slab system will be the main focus in this paper to be compared for its performance with conventional slab system under earthquake. Regarding the floor plan of Sequis Tower basement, re-entrant corner signed for this building is 43.21% which exceeded the allowable re-entrant corner is 15% as stated in ASCE 7-05 Based on that, the horizontal irregularity will be another concern for analysis, otherwise vertical irregularity does not exist for this building. Flat slab system is a system where the slabs use drop panel with shear head as their support instead of using beams. Major advantages of flat slab application are decreasing dead load of structure, removing beams so that the clear height can be maximized, and providing lateral resistance due to lateral load. Whilst, deflection at middle strip and punching shear are problems to be detail considered. Torsion usually appears when the structural member under flexure such as beam or column dimension is improper in ratio. Considering flat slab as alternative slab system will keep the collapse due to torsion down. Common seismic load resisting system applied in the building is a shear wall. Installation of shear wall will keep the structural system stronger and stiffer affecting in reduced displacement under earthquake. Eccentricity of shear wall location of this building resolved the instability due to horizontal irregularity so that the earthquake load can be absorbed. Performing linear dynamic analysis such as response spectrum and time history analysis due to earthquake load is suitable as the irregularity arise so that the performance of structure can be significantly observed. Utilization of response spectrum data for South Jakarta which PGA 0.389g is basic for the earthquake load idealization to be involved in several load combinations stated on SNI 03-1726-2012. The analysis will result in some basic seismic parameters such as period, displacement, and base shear of the system; besides the internal forces of the critical member will be presented. Predicted period of a structure under earthquake load is 0.45 second, but as different slab system applied in the analysis then the period will show a different value. Flat slab system will probably result in better performance for the displacement parameter compare to conventional slab system due to higher contribution of stiffness to the whole system of the building. In line with displacement, the deflection of the slab will result smaller for flat slab than a conventional slab. Henceforth, shear wall will be effective to strengthen the conventional slab system than flat slab system.
Effect of Water-Cement Ratio on the Compressive Strength of Sandcrete Block Blended with Sawdust Ash
The problem of managing agricultural and industrial wastes has become a challenge in recent time. Therefore, research in the area of minimizing waste accumulation through reclamation and recycling has been ignited considering their aesthetic and ecological problems caused by the improper disposal. Areas of research aimed at reducing waste include the use of sawdust ash, rice-husk ash and groundnut-husk ash to partially replace cement in the production of concrete or sandcrete blocks. The use of sawdust ash (SDA) as replacement of cement in the production of sandcrete blocks was investigated. The aim was to determine the percentage of SDA and water-cement ratio that would give the 28-day maximum strength. The sawdust ash was used to partially replace Ordinary Portland Cement (OPC) in various proportions (0%, 5% 10%, 15% and 20%).Cubes were produced using mix ratio 1:4 and water-cement ratios of 0.40, 0.50, 0.55 and 0.60.The cubes were tested at the ages of 7, 14, 21 and 28 days for each proportion of OPC/SDA and water cement ratio. The results indicated that compressive strength of blocks at 28 days was 3.80N/mm2 and 3.50N/mm2 for 5% SDA at water-cement ratios 0.55 and 0.60 respectively. The compressive strength for 10% SDA was 2.87N/mm2 and 3.10N/mm2 at water-cement ratios 0.55 and 0.60 respectively. The 5% and 10% percentage replacements have compressive greater than the required strength of 2.00N/mm2 specified by the Nigerian National Building Code (2006) for non-load bearing walls. By these results sandcrete blocks with up to 10% SDA replacement at water-cement ratios 0.55 and 0.60 can be used for non-load bearing walls.
A Study on Application of Elastic Theory for Computing Flexural Stresses in Preflex Beam
This paper presents the step-by-step procedure for using the Elastic Theory to calculate the internal stresses in composite bridge girder prestressed by the Preflexing Technology, called prebeam in Japan and preflex beam worldwide. Following the Prestressing Technology developed late in the 1930’s, the preflex method of prestressing was invented early in the 1950’s by the Belgian engineer, Abraham Lipski, with assistance from Louis Baes, in Brussels. Preflex beam is a pre-cambered composite beam. Basically, it is a pre-cambered I-shaped steel plate-girder which is bent under preflexion loads using the four-points-bending method such that it becomes flat with no pre-camber left. Following that step, high strength concrete is cast on its lower flange. As the concrete hardens, the preflexion loads are removed. The beam recovers a measure of its camber while the rest of it leads to introduction of compressive stress in the concrete. Pouring the upper flange concrete completes the construction. As far as the depth and deflection limitations are the governing requirements in the design process, preflex beam is a suitable option to meet the requirements to a large extent. When it comes to analyzing flexural members in terms of internal stresses, the Elastic Theory has been the convenient method of dealing with similar cases. Researches carried out on the serviceability of the Elastic Theory for predicting internal stresses in preflex beam have concluded that the theory can be satisfactorily used to predict the internal stresses which occur in preflex beam during the preflexion operation and the service life of the beam. Unlike the conventional composite members, preflex beam undergoes different steps during construction; namely, preflexion, lower flange concrete casting, preflexion release, and lastly the upper flange concrete casting. Since the materials used and loading conditions vary from a step to another, stresses are calculated in every single phase under the loads in action with section properties involved in the specific case. Stress accumulation gives the present stress in a section of interest. Graphical concrete presence in the section implies prestress loss due to creep and shrinkage; however, more work is required to be done in this field. In addition to the graphical presentation of this application, this paper further discusses important notes of graphical comparison between the results of an experimental-only research carried out on a preflex beam, with the results of simulation for an identical beam using Finite Element Modeling (FEM) by the author.
Finite Element Analysis of the Ordinary Reinforced Concrete Bridge Piers
Most of the concrete bridges in Nepal constructed during 90's and before are made up of low strength ordinary concrete which might be one of the reasons for damage in higher magnitude earthquake. Those bridges were designed by the outdated bridge codes which might not account the large seismic loads. This research investigates the seismic vulnerability of the existing single column ordinary concrete bridge pier by finite element modeling, using the software Seismostruct. The existing bridge pier capacity has been assessed using nonlinear pushover analysis and performance is compared after retrofitting those pier models with CFRP. Furthermore, the seismic evaluation was made by conducting cyclic loading test at different drift percentage. The performance analysis of bridge pier by nonlinear pushover analysis is further validated by energy dissipation phenomenon measured from the hysteric loop for each model of ordinary concrete piers.
Design of an Automatic Saw Cutting Machine for Wood and Aluminum
The uses of wood in furniture, building, bridges and aluminum in transportation and construction, make aluminum and forest economy a prominent matter in North America. Machines available to date to cut the aforementioned materials are mostly industry oriented with complex structure and operations which require special training and skill. Furthermore, requirements such as pneumatics, 3-phase supply are associated with cost, maintenance, and safety hazards. Power saws are very useful tools used to cut and shape materials; however, they can cause serious hand injuries. Operator’s hands in table saw are vulnerable as they are used to guide pieces into the saw. Apart from hands, saw operator is also prone to material being kicked back out of the saw or sustain eye or respiratory injuries due to rapidly flying sawdust and other debris. In this paper, design of an automatic saw cutting machine has been proposed to ensure safety, portability, usage at domestic level and capability to cut both aluminum and wood. This paper demonstrates detailed Mechanical design in SOLIDWORKS and Control Systems using Programmable Logic Controller (PLC), based on the aforementioned design objectives.
An Overview of Electronic Waste as Aggregate in Concrete
Rapid growth of world population and widespread urbanization has remarkably increased the development of the construction industry which caused a huge demand for sand and gravels. Environmental problems occur when the rate of extraction of sand, gravels, and other materials exceeds the rate of generation of natural resources. Therefore, an alternative source is essential to replace the materials used in concrete. Nowadays electronic products have become an integral part of daily life which provides with more comfort, security, easy exchange of information. These electronic wastes (E-Wastes) materials have serious human health concerns and require extreme care in its disposal to avoid adverse impacts. Disposal or dumping of these electronic wastes also causes major issues because it is highly complex to handle and often contains highly toxic chemicals such as lead, cadmium, mercury, beryllium, Brominates Flame Retardants (BFRs), Poly Vinyl Chloride (PVC) and phosphorus compounds. These E-Wastes can be incorporated in concrete to make sustainable environment. This paper deals with the composition, preparation of E-Waste material and its properties. This paper also provides a detailed literature review on the behavior of concrete with incorporation of E-Wastes. Many research shows a strong possibility of using E-waste as a substitute of aggregates in concrete. As a result of this tends to decrease the use natural aggregates in concrete and a prime importance where substitute of aggregates can be explored.
Influence of Alccofine on Semi-Light Weight Concrete under Accelerated Curing and Conventional Curing Regimes
This paper deals with the performance of semi-light weight concrete, prepared by using wood ash pellets as coarse aggregates which were improved by partial replacement of cement with Alccofine. Wood ash is a tamarind bark combustion product composed of fine particles that falls in the bottom of the modern rice mill dryers. Alccofine is a mineral admixture which contains high glass content obtained through the process of controlled granulation. These cementitious materials are much finer than cement and carries its own pozzolanic property. Therefore, cement could be replaced by Alccofine as 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, and 70% to enhance the strength and durability properties of concrete. High Range Water reducing admixtures (HRWA) was used in these mixes which were dosed up to 1.5% weight of the total cementitious materials content. It also develops the weaker transition zone into more impermeable layer. Specimens were subjected to accelerated curing method as well as conventional curing method. Experimental results were compared and reported that a maximum 28th day compressive strength of 32.6 MPa has achieved at 30% replacement level with a density of 2200 kg/m³ in conventional curing while in accelerated curing, the maximum compressive strength has achieved at 40% replacement level. Rapid chloride penetration test output results of conventional curing method for 0% and 70% gives 3296.7 and 545.6 coulombs.
Seismic Performance of Benchmark Building Installed with Semi-Active Dampers
The seismic performance of 20-storey benchmark building with semi-active dampers is investigated under various earthquake ground motions. The Semi-Active Variable Friction Dampers (SAVFD) and Magnetorheological Dampers (MR) are used in this study. A recently proposed predictive control algorithm is employed for SAVFD and a simple mechanical model based on a Bouc–Wen element with clipped optimal control algorithm is employed for MR damper. A parametric study is carried out to ascertain the optimum parameters of the semi-active controllers, which yields the minimum performance indices of controlled benchmark building. The effectiveness of dampers is studied in terms of the reduction in structural responses and performance criteria. To minimize the cost of the dampers, the optimal location of the damper, rather than providing the dampers at all floors, is also investigated. The semi-active dampers installed in benchmark building effectively reduces the earthquake-induced responses. Lesser number of dampers at appropriate locations also provides comparable response of benchmark building, thereby reducing cost of dampers significantly. The effectiveness of two semi-active devices in mitigating seismic responses is cross compared. Among two semi-active devices majority of the performance criteria of MR dampers are lower than SAVFD installed with benchmark building. Thus the performance of the MR dampers is far better than SAVFD in reducing displacement, drift, acceleration and base shear of mid to high-rise building against seismic forces.
3D Non-Linear Model Describing the Behaviour of Peripheral High Capacity Saw-Tooth Connectors Subjected to Compressive Load
This contribution aims to demonstrate the behaviour of a high capacity saw-tooth connectors fixed at the edges of a slender reinforced concrete slab. The connectors are subjected to compressive load and mainly designed to transfer shear forces into the slab either from steel truss or cable, as in truss bridge or cable stayed bridge. A 3D finite element model is carried out in ANSYS Workbench environment to simulate the specimen. The description of non-linear material behaviour is implemented by using an elasto-plastic model. The material model is defined by adopting Menetrey-Willam failure criterion and non-associated flow rule. Hardening/softening law is obtained by using power hardening function and fracture based function, which define the behaviour of concrete based on the stressstrain relation. The contacts between the concrete and the connector are defined by Augmented formulation, while multi-point-constraint formulation (MPC) is used to define the contact of reinforcement rebars-concrete. Hex mesh is chosen to mitigate the calculation cost and get a better result, whereas the size of mesh is determined to be in line with the fracture energy limits. The model shows a good agreement with the experimental force – displacement relation, with discrepancy of 2-5%. Moreover, the model gives the same values of the strain of the concrete attained from the experiments, where many strain gauges are distributed around the connector. It is observed that the behaviour of the connector is brittle, where the failure occurs after moving the connector 1.4 mm. However, the load capacity of the connector is higher than the conventional types of connectors, where it reaches 1994 KN. An early test had been carried out on the saw tooth connector embedded in the middle of the specimen showed that the concrete’s failure formed as a wedge surrounding the connector. The width of that wedge is relatively wider than the one acquired from the test of the peripheral connectors. Therefore, based on many tests and models, a study is conducted intending to increase the ductility of the concrete around the saw-tooth connector by allocating double headed shear studs around it. The allocation of the studs depends on the shear stresses and minimum principal stresses in the concrete. The results of the model indicate that the heads of the studs increase the confinement of the concrete and hence increase significantly the load capacity of the connector by almost 19%. Even though, the ductility of the concrete is increased, the maximum displacement of the connector decreased. The difference of the displacement happens, because of the crushing of the concrete between the lowest teeth of the connector and the head of the studs.
Simulation of Piezoelectric Laminated Smart Structure under Strong Electric Field
Piezoelectric materials usually behave very significant material nonlinear effects under strong electric fields. In order to give a precise prediction of piezolaminated smart structures under large electric field, this paper develops a finite element (FE) model accounting for material nonlinearity (piezoelectric part) based on the first order shear deformation (FSOD) hypothesis. The proposed FE model is first validated by both experimental and numerical examples from the literature. Afterwards, it is applied to simulate for plate and shell structures with multiple piezoelectric patches under strong applied electric field. From the simulation results, it shows that large discrepancies occur between linear and material nonlinear predictions for piezoelectric laminated structures driving at strong electric field. Therefore, material nonlinearity should be taken into account for piezoelectric structures under strong electric.
Limit State of Heterogeneous Smart Structures under Unknown Cyclic Loading
This paper presents a numerical solution, namely limit and shakedown analysis, to predict the safety state of smart structures made of heterogeneous materials under unknown cyclic loadings, for instance, the flexure hinge in micro-positioning stage driven by piezoelectric actuator. In combination of homogenization theory and finite-element method (FEM), the safety evaluation problem is converted to a large-scale nonlinear optimization programming for an acceptable bounded loading as the design reference. Furthermore, a general numerical scheme integrated with the FEM and interior-point-algorithm based optimization tool is developed, which makes the practical application possible.
Seismic Performance of Concrete Moment Resisting Frames in Western Canada
Performance-based seismic design concepts are increasingly being adopted in various jurisdictions. While the National Building Code of Canada (NBCC) is not fully performance-based, it provides some features of a performance-based code, such as displacement control and objective-based solutions. Performance evaluation is an important part of a performance-based design. In this paper, the seismic performance of a set of code-designed 4, 8 and 12 story moment resisting concrete frames located in Victoria, BC, in the western part of Canada at different hazard levels namely, SLE (Service Level Event), DLE (Design Level Event) and MCE (Maximum Considered Event) has been studied. The seismic performance of these buildings has been evaluated based on FEMA 356 and ATC 72 procedures, and the nonlinear time history analysis. Pushover analysis has been used to investigate the different performance levels of these buildings and adjust their design based on the corresponding target displacements. Since pushover analysis ignores the higher mode effects, nonlinear dynamic time history using a set of ground motion records has been performed. Different types of ground motion records, such as crustal and subduction earthquake records have been used for the dynamic analysis to determine their effects. Results obtained from push over analysis on inter-story drift, displacement, shear and overturning moment are compared to those from the dynamic analysis.
Model-Based Fault Diagnosis in Carbon Fiber Reinforced Composites Using Particle Filtering
Carbon fiber reinforced composites (CFRP) used as aircraft structure are subject to lightning strike, putting structural integrity under risk. Indirect damage may occur after a lightning strike where the internal structure can be damaged due to excessive heat induced by lightning current, while the surface of the structures remains intact. Three damage modes may be observed after a lightning strike: fiber breakage, inter-ply delamination and intra-ply cracks. The assessment of internal damage states in composite is challenging due to complicated microstructure, inherent uncertainties, and existence of multiple damage modes. In this work, a model based approach is adopted to diagnose faults in carbon composites after lighting strikes. A resistor network model is implemented to relate the overall electrical and thermal conduction behavior under simulated lightning current waveform to the intrinsic temperature dependent material properties, microstructure and degradation of materials. A fault detection and identification (FDI) module utilizes the physics based model and a particle filtering algorithm to identify damage mode as well as calculate the probability of structural failure. Extensive simulation results are provided to substantiate the proposed fault diagnosis methodology with both single fault and multiple faults cases. The approach is also demonstrated on transient resistance data collected from a IM7/Epoxy laminate under simulated lightning strike.
Impact of Joule Heating on the Electrical Conduction Behavior of Carbon Composite Laminates under Simulated Lightning Strike
Increasing demands for high strength and lightweight materials in aircraft industry prompted the wide use of carbon composites in recent decades. Carbon composite laminates used on aircraft structures are subject to lightning strikes. Unlike its metal/alloy counterparts, carbon fiber reinforced composites demonstrate smaller electrical conductivity, yielding more severe damages due to Joule heating. The anisotropic nature of composite laminates makes the electrical and thermal conduction within carbon composite laminates even more complicated. Good understanding of the electrical conduction behavior of carbon composites is the key to effective lightning protection design. The goal of this study is to numerically and experimentally investigate the impact of ultra-high temperature induced by simulated lightning strike on the electrical conduction of carbon composites. A lightning simulator is designed to apply standard lightning current waveform to composite laminates. Multiple carbon composite laminates made from IM7 and AS4 carbon fiber are tested and the transient resistance data is recorded. A microstructure based resistor network model is developed to describe the electrical and thermal conduction behavior, with consideration of temperature dependent material properties. Material degradations such as thermal and electrical breakdown are also modeled to include the effect of high current and high temperature induced by lightning strikes. Good match between the simulation results and experimental data indicates that the developed model captures the major conduction mechanisms. A parametric study is then conducted using the validated model to investigate the effect of system parameters such as fiber volume fraction, inter-ply interface quality, and lightning current waveforms.
Particleboard Production from Atmospheric Plasma Treated Wheat Straw Particles
Particle boards have being used in the civil engineering as a decking for load bearing and non-load bearing vertical walls and horizontal panels (e. g. floors, ceiling, roofs) in a large scale. When the straw is used as non-wood material for manufacturing of lignocellulosic panels, problems with wax layer on the surface of the material can occur. Higher percentage of silica and wax cause the problems with the adhesion of the adhesive and this is the reason why it is necessary to break the surface layer for the better bonding effect. Surface treatment of the particles cause better mechanical properties, physical properties and the overall better results of the composite material are reached. Plasma application is one possibility how to modify the surface layer. The aim of this research is to modify the surface of straw particles by using cold plasma treatment. Surface properties of lignocellulosic materials were observed before and after cold plasma treatment. Cold plasma does not cause any structural changes deeply in the material. There are only changes in surface layers, which are required. Results proved that the plasma application influenced the properties of surface layers and the properties of composite material.
Finite Element Analysis of Piezolaminated Structures with Both Geometric and Electroelastic Material Nonlinearities
Piezoelectric laminated smart structures can be subjected to the strong driving electric field, which may result in large displacements and rotations. In one hand, piezoelectric materials usually behave very significant material nonlinear effects under strong electric fields. On the other hand, thin-walled structures undergoing large displacements and rotations exist nonnegligible geometric nonlinearity. In order to give a precise prediction of piezo laminated smart structures under the large electric field, this paper develops a finite element (FE) model accounting for material nonlinearity (piezoelectric part) and geometric nonlinearity based on the first order shear deformation (FSOD) hypothesis. The proposed FE model is first validated by both experimental and numerical examples from the literature. Afterwards, it is applied to simulate for plate and shell structures with multiple piezoelectric patches under the strong applied electric field. From the simulation results, it shows that large discrepancies occur between linear and nonlinear predictions for piezoelectric laminated structures driving at the strong electric field. Therefore, both material and geometric nonlinearities should be taken into account for piezoelectric structures under strong electric.
Nonlinear Modelling and Analysis of Piezoelectric Smart Thin-Walled Structures in Supersonic Flow
Thin-walled structures are used more and more widely in modern aircrafts and some other structures in aerospace field nowadays. Accompanied by the wider applications, the vibration of the structures has been a bigger problem. Because of the direct and converse piezoelectric effect, piezoelectric materials combined to host thin-walled structures, named as piezoelectric smart structures, can be an effective way to suppress the vibration. So, an accurate model for piezoelectric thin-walled structures in air flow is necessary and important. In our recent work, an electromechanical coupling nonlinear aerodynamic finite element model of piezoelectric smart thin-walled structures is built based on the Reissner-Mindlin plate theory and first-order piston theory for aerodynamic pressure of supersonic flow. Von Kármán type nonlinearity is considered in the present model. Finally, the model is validated by experimental and numerical results from the literature, which can describe the vibration of the structures in supersonic flow precisely.
Experimental Studies of Sigma Thin-Walled Beams Strengthen by CFRP Tapes
The review of selected methods of strengthening of steel structures with carbon fiber reinforced polymer (CFRP) tapes and the analysis of influence of composite materials on the steel thin-walled elements are performed in this paper. The study is also focused to the problem of applying fast and effective strengthening methods of the steel structures made of thin-walled profiles. It is worth noting that the issue of strengthening the thin-walled structures is a very complex, due to inability to perform welded joints in this type of elements and the limited ability to applying mechanical fasteners. Moreover, structures made of thin-walled cross-section demonstrate a high sensitivity to imperfections and tendency to interactive buckling, which may substantially contribute to the reduction of critical load capacity. Due to the lack of commonly used and recognized modern methods of strengthening of thin-walled steel structures, authors performed the experimental studies of thin-walled sigma profiles strengthened with CFRP tapes. The paper presents the experimental stand and the preliminary results of laboratory test concerning the analysis of the effectiveness of the strengthening steel beams made of thin-walled sigma profiles with CFRP tapes. The study includes six beams made of the cold-rolled sigma profiles with height of 140 mm, wall thickness of 2.5 mm, and a length of 3 m, subjected to the uniformly distributed load. Four beams have been strengthened with carbon fiber tape Sika CarboDur S, while the other two were tested without strengthening to obtain reference results. Based on the obtained results, the evaluation of the accuracy of applied composite materials for strengthening of thin-walled structures was performed.
Testing of the Decreasing Bond Strength of Polyvinyl Acetate Adhesive by Low Temperatures
When using wood products bonded by polyvinyl acetate, glues such as windows are the most limiting element of degradation of the glued joint due to weather changes. In addition to moisture and high temperatures, the joint may damage the low temperature below freezing point, where dimensional changes in the material and distortion of the adhesive film occur. During the experiments, the joints were exposed to several degrees of sub-zero temperatures from 0 °C to -40 °C and then to compare how the decreasing temperature affects the strength of the joint. The experiment was performed on wood beech samples (Fagus sylvatica), bonded with PVAc with D3 resistance and the shear strength of bond was measured. The glued and treated samples were tested on a laboratory testing machine, recording the strength of the joint. The statistical results have given us information that the strength of the joint gradually decreases with decreasing temperature, but a noticeable and statistically significant change is achieved only at very low temperatures.
The Effect of Transparent Oil Wood Stain on the Colour Stability of Spruce Wood during Weathering
Nowadays the use of wood, both indoors and outdoors, is constantly increasing. However wood is a natural organic material and in the exterior is subjected to a degradation process caused by abiotic factors (solar radiation, rain, moisture, wind, dust etc.). This process affects only surface layers of wood but neglecting some of the basic rules of wood protection leads to increased possibility of biological agents attack and thereby influences a function of the wood element. The process of wood degradation can be decreased by proper surface treatment, especially in the case of less naturally durable wood species, as spruce. Modern coating systems are subjected to many requirements such as colour stability, hydrophobicity, low volatile organic compound (VOC) content, long service life or easy maintenance. The aim of this study is to evaluate the colour stability of spruce wood (Picea abies), as the basic parameter indicating the coating durability, treated with two layers of transparent natural oil wood stain and exposed to outdoor conditions. The test specimens were exposed for 2 years to natural weathering and 2000 hours to artificial weathering in UV-chamber. The colour parameters were measured before and during exposure to weathering by the spectrophotometer according to CIELab colour space. The comparison between untreated and treated wood and both testing procedures was carried out. The results showed a significant effect of coating on the colour stability of wood, as expected. Nevertheless, increasing colour changes of wood observed during the exposure to weathering differed according to applied testing procedure - natural and artificial.
Forced Vibration of a Planar Curved Beam on Pasternak Foundation
The objective of this study is to investigate the forced vibration analysis of a planar curved beam lying on elastic foundation by using the mixed finite element method. The finite element formulation is based on the Timoshenko beam theory. In order to solve the problems in frequency domain, the element matrices of two nodded curvilinear elements are transformed into Laplace space. The results are transformed back to the time domain by the well-known numerical Modified Durbin’s transformation algorithm. First, the presented finite element formulation is verified through the forced vibration analysis of a planar curved Timoshenko beam resting on Winkler foundation and the finite element results are compared with the results available in the literature. Then, the forced vibration analysis of a planar curved beam resting on Winkler-Pasternak foundation is conducted.