Substructure Design Research Articles

Ground improvement and foundation practice for Persian Gulf Bridge (causeway); Bandar Abbas Harbor–Qeshm Island

ABSTRACTNational Persian Gulf Bridge is a communication route between Bandar Abbas port and Qeshm Island located on the southern border of Iran. This causeway has important role for facilitating the transportation system between Qeshm Island and mainland, i.e., Bandar Abbas. Based on geotechnical and geological site investigation records, the bridge is located on the deposits with high seismic possibility and subsequently significant dynamic loading. Therefore, adequate substructure design of this bridge as an offshore project is realized as a major requirement. The geophysical and geotechnical investigations have been done to obtain the subsoil characteristics of the project site. For this purpose, 18 boreholes have been performed to do in situ tests and extract samples for laboratory testings. Data synthesis indicates that in the zones close to Qeshm Island and in the deeper parts of the sea, the strata is made of clay with loose sands and some depths, with silty sands. Hence, instability issues, including the low bearing capacity and the high differential settlement, are significant aspects in analysis and design of substructure for this project. Also, in this paper, the subsoil conditions have been studied from in situ tests such as standard penetration test (SPT) and cone penetration test (CPT) results in order to achieve an appropriate foundation system. Moreover, the necessity of the ground improvement of the site has been investigated to propose an efficient technique for safe and secure construction. Based on the analysis and methods screened, the vibro-replacement method is considered as a suitable and efficient ground improvement method for this project.

Collapse Behavior of RC Column-Beam Sub-Structure with External Prestressing Tendons

Previous studies indicated that the external prestressing tendons can effectively improve the deformability and bearing capacity of RC frames. However, how to utilize the external prestressing tendons to prevent the increase of deformation of the structure with catenary action in the process of collapse needs further study. Using an analytical method for the stress variations of external prestressing tendons based on structural deformation, the deflection and stress of beam-column sub-structureunder the failure of RC column during elastic and plastic stages are studied, the calculation of ultimate bearing capacity considering catenary action are also presented which provide a basis for collapse-resistant design of beam-column sub-structures.

Cross-wind fatigue analysis of a full scale offshore wind turbine in the case of wind–wave misalignment

Wind–wave misalignment is often necessary to consider during the design of offshore wind turbines due to excitation of side–side vibration and the low aerodynamic damping in that direction. The measurements from a fully instrumented 3.6MW pitch regulated-variable speed offshore wind turbine were used for the estimation of the side–side fatigue loads at the tower bottom. The joint wind–wave distribution and the distribution of the wind–wave misalignment angles were considered. The side–side fatigue at the tower bottom and the damping from site measurements are presented as function of the misalignment angles. A model of the same wind turbine was set-up and simulations with the aero-hydro-servo-elastic code HAWC2 were performed to investigate the effect of damping on the side–side fatigue. Turbulent wind field, irregular waves and flexible soil are used in the simulations based on site-measurements. The aim of the current study is to examine the sensitivity of the side–side fatigue to the wind–wave misalignment and different values of additional offshore damping in the system. It was found that the additional offshore damping of the physical system may be higher than what is typically used in offshore wind turbine sub-structure design, due to the low sensitivity of the measured side–side fatigue loads to the misalignment angle. Choice of an accurate damping value implemented in the model during the design of the wind turbine sub-structure can lead to material and cost savings.

Design and Analysis of Jacket Substructures for Offshore Wind Turbines

This study focused on investigating various existing types of offshore jacket substructures along with a proposed twisted-tripod jacket type (modified jacket (MJ)-structures). The architectures of the three-leg structure, as well as the patented twisted jacket structure motivated the design of the proposed MJ-structures. The dimensions of the structures were designed iteratively using static stress analysis to ensure that all structures had a similar level of load-carrying capability. The numerical global buckling analyses were performed for all structures after the validation by the scaled-down experiments. The local buckling strength of all compressive members was analyzed using the NORSOK standard. The results showed that the proposed MJ-structures possess excellent structural behavior and few structural nodes and components competitive with the patented twisted jacket structures, while still maintaining the advantages of low material usage similar to the three-leg jacket structures. This study provides alternatives for the initial selection and design of offshore wind turbine substructures for green energy applications.

Compliant structures-based wing and wingtip morphing devices

Purpose The purpose of this paper is to provide an overview of the design and experimental work of compliant wing and wingtip morphing devices conducted within the EU FP7 project NOVEMOR and to demonstrate that the optimization tools developed can be used to synthesize compliant morphing devices. Design/methodology/approach The compliant morphing devices were “designed-through-optimization”, with the optimization algorithms including Simplex optimization for composite compliant skin design, aerodynamic shape optimization able to take into account the structural behaviour of the morphing skin, continuum-based and load path representation topology optimization methods and multi-objective optimization coupled with genetic algorithm for compliant internal substructure design. Low-speed subsonic wind tunnel testing was performed as an effective means of demonstrating proof-of-concept. Findings It was found that the optimization tools could be successfully implemented in the manufacture and testing stage. Preliminary insight into the performance of the compliant structure has been made during the first wind tunnel tests. Practical implications The tools in this work further the development of morphing structures, which when implemented in aircraft have potential implications to environmentally friendlier aircrafts. Originality/value The key innovations in this paper include the development of a composite skin optimization tool for the design of highly 3D morphing wings and its ensuing manufacture process; the development of a continuum-based topology optimization tool for shape control design of compliant mechanisms considering the stiffness and displacement functions; the use of a superelastic material for the compliant mechanism; and wind tunnel validation of morphing wing devices based on compliant structure technology.

5MW급 해상풍력 하부구조물 설계 및 해석에 관한 연구

5MW급 해상풍력 하부구조물 설계 및 해석에 관한 연구

Insulation - Technical Analysis of Ground Connections and its Impact on the Solution of Substructure Design Details

Most industrial hall type buildings are large. The accurate design of the substructures construction is influenced by many entry parameters from the standpoint of structural analysis, building thermal technology, building hydro-insulation technology and anti-radon measures. By respecting these specific requirements of individual science disciplines, the symbiosis expressing the optimal solution in the theory of structural production of buildings are presented.

Chemical analysis and X-ray diffraction assessment of stabilized expansive soils

The long-term viability of many construction projects is heavily dependent on the soundness of the underlying subgrade soil which needs to be capable of supporting loads from structures without undergoing excessive deformation or volume changes. However, in certain locations geotechnical engineers face repeated problems in the design of substructures due to the presence of expansive soils. Light structures are especially susceptible to damage in such situations which can result in cracks in walls, beams, columns and on-grade slabs. One extensively used way of overcoming such problems is to improve the soil by stabilizing it with cement and/or lime which prevents this unwanted behavior. Most previous research conducted on expansive soils focused on studying the effects of treatment on the physical properties of the soil without detailed examination of the physicochemical mechanism of the process, although some studies surveyed the effect of the treatment using cement and lime on the mineralogical composition and newly formed pozzolanic compounds. In this research the mineralogical changes due to lime and cement additions to two different expansive soils from Saudi Arabia, in particular, were investigated using X-ray diffraction. The results of this work indicate that addition of lime or cement to the soils tested resulted in the formation of pozzolanic compounds, namely, calcium silicate hydrate and calcium aluminate hydrate together with calcite (CaCO3). The soil improvements are compared for cement and lime. Changes in potassium, aluminum and silicon were also determined and interpreted in terms of the soil mineralogy. It was concluded that pozzolanic compounds play a significant role in reducing the swelling and increasing the strength.

Multichannel enhanced Faraday rotations in magnetic heterostructures

Transmittance and Faraday rotation (FR) spectra of one-dimensional magnetic heterostructures are investigated using 4 by 4 transfer matrix method. It is revealed that in a simple magnetic heterostructure the enhanced FR at a desired wavelength can be realized considering a special design of substructures and adjusting the thicknesses of constituent magnetic layers. In addition, a complex magnetic heterostructure with capability of providing the multichannel enhanced FRs at desired wavelengths is introduced. It is shown that such a heterostructure could support high transmittance enhanced FRs at telecommunication wavelengths of 1300 and 1550nm, simultaneously. The results may have potential applications in designing the multi-function single magneto-optical devices such as multichannel Faraday rotators and wavelength division multiplexing systems.

Influence of Substructure Design and Occlusal Reduction on the Stress Distribution in Metal Ceramic Complete Crowns: 3D Finite Element Analysis

Occlusal reduction is considered a fundamental step for providing adequate and uniform space for the ceramic prosthesis; however, a flat occlusal surface is usually found. The prosthesis design influences the resistance to deformation and the stress state within the ceramic. This finite element (FE) study analyzes the influence of changing the substructure design on the stress distribution of a metal-ceramic crown in a premolar tooth with three types of occlusal reduction. Each part of three-dimensional metal ceramic complete crown models was designed according to the space provided by different levels of occlusal reduction and the same external morphology of the tooth. Three models were designed: (1) correct occlusal reduction with a uniform thickness of the substructure (0.3 mm) and the veneering porcelain (1.5 mm); (2) flat occlusal reduction with different thicknesses of veneering porcelain to produce a uniform substructure; and (3) a flat occlusal reduction with different thicknesses of substructure for a uniform thickness of veneering porcelain. Stress distributions were very similar in the three models. The highest tensile stresses were concentrated immediately below the midline fissure in both the veneering porcelain and the metal alloy substructure. Although models with flat occlusal reduction had lower stress values, this preparation results from a reduction that removes a greater amount of sound tissue, which may increase the probability of dental pulp injury. Occlusal reduction must be anatomic; however, when a flat occlusal reduction already exists, the substructure must reproduce the correct anatomic form to allow a uniform thickness of the veneering porcelain.

Evaluation of Unknown Foundations of Bridges Subjected to Scour

Missing substructure information has impeded the safety assessment of bridges with unknown foundations, especially for scour-prone bridges. An approach based on artificial neural networks (ANNs) was developed to identify the inherent patterns in the substructure design of bridges with commonly available evidence (e.g., geometric characteristics of superstructures, loading conditions, soil properties, year built, and location) and then to generalize them further to bridges with unknown foundations. The proposed ANN models were trained with information collected for an inventory of bridges with available foundation records located in the Bryan District of the Texas Department of Transportation. Results showed that the proposed ANN models were able to make successful predictions about the foundation type and the embedment depth for deep foundations. In addition, the degree of uncertainty in the models’ predictions was evaluated by performing the random subsampling method. Graphs of the probability of exceedance were generated that allowed for factoring the predicted pile depth on the basis of a reasonable probability of failure caused by scour. As a consequence, departments of transportation can adopt a similar methodology to reclassify the bridges with unknown foundations included in the National Bridge Inventory.

Comparison of Totally Prefabricated Bridge Substructure Designed According to Korea Highway Bridge Design (KHBD) and AASHTO-LRFD

The purpose of this study was to investigate the design comparison of totally prefabricated bridge substructure system. Prefabricated bridge substructure systems are a relatively new and versatile alternative in substructure design that can offer numerous benefits. The system can reduce the work load at a construction site and can result in shorter construction periods. The prefabricated bridge substructures are designed by the methods of Korea Highway Bridge Code (KHBD) and load and resistance factor design (AASHTO-LRFD). For the design, the KHBD with DB-24 and DL-24 live loads is used. This study evaluates the design method of KHBD (2005) and AASHTO-LRFD (2007) for totally prefabricated bridge substructure systems. The computer program, reinforced concrete analysis in higher evaluation system technology was used for the analysis of reinforced concrete structures. A bonded tendon element is used based on the finite element method, and can represent the interaction between the tendon and concrete of a prestressed concrete member. A joint element is used in order to predict the inelastic behaviors of segmental joints. This study documents the design comparison of totally prefabricated bridge substructure and presents conclusions and design recommendations based on the analytical findings.

Fracture resistance of different metal substructure designs for implant-supported porcelain-fused-to-metal (PFM) crowns

Background/purposeThis study evaluated the fracture resistance of different metal substructure designs for implant-supported porcelain-fused-to-metal (PFM) crowns. Materials and methodsEighteen PFM crowns were fabricated using different metal substructure designs and were conventionally cemented on an implant abutment analog. The crowns were divided according to the metal substructure design for manufacturing the metal framework into three groups of six specimens each: Group A had a minimum required thickness; Group B had a conventional design; and Group C had a wrinkled design. After applying a load of 200 N at a frequency of 2 Hz with 300,000 cycles of dynamic loading, all specimens were tested for fracture resistance using compression loading on the buccal functional cusp. ResultsAmong these three groups, Groups A and B, respectively, had the minimum and maximum fracture resistance strengths. Respective data for Groups A, B, and C were 111.13 ± 27.15 kg, 236.13 ± 39.21 kg, and 188.63 ± 12.10 kg. Statistically significant differences were observed among the three groups (P < 0.05). ConclusionThese results confirm that the conventional design had the best fracture resistance, and an excessively thick porcelain layer can cause crown fracture. However, there was no obvious proof that the wrinkled design had better fracture resistance than the conventional design. Therefore, the theory that PFM can provide better support requires further corroboration.

Influence of substructure design, veneer application technique, and firing regime on the in vitro performance of molar zirconia crowns

ObjectivesThe aim of this in vitro study was to evaluate the influence of substructure design, veneer application technique, and firing regime on the failure and fracture resistance of molar zirconia crowns. MethodsSix groups (n=8/group) of zirconia crowns were fabricated in simple core (SC) or anatomically reduced (AR) design, veneered with different feldspathic or glass ceramic materials, and defined according to the application technique and firing regime (LT: layering technique; LT_L: LT with long-term cooling; PT: press technique; DV: digital veneering technique). The following groups were investigated: SCLT, ARLT, SCLT_L, SCPT, ARPT, ARDV. Crowns were adhesively bonded to polymethylmethacrylate abutment teeth and subjected to thermal cycling (TC: 2×3000×5°/55°) and mechanical loading (ML: 1.2×106; 50N; 1.6Hz) in a chewing simulator with metal-ceramic molar crowns as antagonists. Failures were monitored and fracture resistance determined after aging. Data were statistically analyzed (one-way analysis of variance, ANOVA; post hoc Bonferroni, α=0.05). Crowns were subjected to scanning electron microscopy for fractographic failure analysis. ResultsFailures (chipping, cracks) during TCML were observed in groups SCLT (2×), ARDV (2×) and SCLT_L (1×). Defect sizes varied between 3.5mm (SCLT: crack) and 30.0mm2 (SCLT_L: chipping). Mean (SD) fracture forces ranged between 1529.0 (405.2)N for SCPT and 2372.3 (351.8)N for ARDV. SignificanceThe failure frequency of veneered zirconia crowns could be reduced by using anatomically reduced substructures, the press veneering technique, and an adapted cooling protocol. Fracture resistance increased with use of anatomically reduced substructures and the digital veneering technique.

The effect of translucency of Y-TZP based all-ceramic crowns fabricated with different substructure designs

PurposeTo analyse the effect of translucency of Y-TZP based all-ceramic crowns fabricated with different substructure thicknesses and extensions. The effect of restoration shading is also investigated. Materials and methodsA maxillary right central incisal typodont tooth was prepared and a die was fabricated with Type IV stone after making impression. Horizontally and vertically reduced substructure extensions were designed at the facial cervical part with 0.3mm and 0.5mm thick Lava Y-TZP. Each substructure was fabricated with two different shades, FS1 and FS7. A1 shade veneering porcelain was applied on FS1 shade Y-TZP substructures and D3 shade veneering porcelain was applied on FS7 shade Y-TZP substructures with lost wax and press ceramic technique. Ten specimens were fabricated for a total of 8 groups. The cervical and body color of specimens were analysed with a spectrophotometer, after placing specimens on the two different colored abutment teeth using translucent try-in cement. The data were obtained in CIELAB color coordinates L*a*b*, and ΔE* through the test specimens over ND1 and ND8 shade abutments were calculated. ResultsAt the cervical area, there was a significant difference on substructure extension (P<0.001). At the body area, results were borderline on substructure thickness (P=0.05) and there was a significant difference on restoration shade (P=0.001). ConclusionsVertical reduction design of Y-TZP substructure could increase ΔE* at the cervical area. Decreasing thickness of Y-TZP substructure may increase ΔE* at the body area. Increasing the value of Y-TZP based-all ceramic crown shade could increase ΔE* at the body area. Clinical significanceThe translucency of a Y-TZP based all-ceramic crowns may influence its esthetic outcome when it is used on a discolored abutment tooth.Clinicians should be aware of the effect of substructure design on the translucency of Y-TZP based all-ceramic crowns.

Maxillary implant-supported bar overdenture and mandibular implant-retained fixed denture using CAD/CAM technology and 3-D design software: A clinical report

The implant-supported bar overdenture and the implant-retained fixed complete denture are appropriate treatment choices for patients with inadequate bone volume in the posterior maxilla and mandible, respectively. Computer-aided design/computer-aided manufacturing (CAD/CAM) technology has broadened the scope and application of those treatment options, allowing for prosthodontically-driven implant placement and ideal substructure design for optimal esthetics and biomechanics. This report describes the fabrication of a maxillary implant-supported milled titanium bar with attachments and an overdenture, and a mandibular implant-retained fixed complete denture with milled titanium substructure.

A Simplified Approach to Bridge Substructure Design

Strut-and-tie modeling is an analysis and design tool for reinforced concrete elements in which it may be assumed that internal stresses are transferred through a truss mechanism. The tensile ties and compressive struts serve as truss members connected by nodal zones. The internal truss idealized by the strut-and-tie model implicitly account for the distribution of both flexure and shear. In 1998, the AASHTO LRFD Bridge Specifications (1998) incorporated the strut-and-tie modeling procedure for the analysis and design of deep reinforced concrete members where sectional design approaches are not valid. In most instances, hammerhead piers can be defined as deep reinforced concrete members and therefore, should be designed using the strut-and-tie modeling approach. However, most bridge designers have not embraced the strut-and-tie model due to the unfamiliarity with the design procedure, the inability to check the truss model’s validity (without laboratory tests or a finite element model), and the time it takes to complete the strut-and-tie model analysis and design. Therefore, with the formulation of a well-defined strut-and-tie modeling procedure, practicing engineers will become more comfortable with the design method and employ the method more often and more consistently. This paper presents a uniform design procedure for employing strut-and-tie modeling for hammerhead piers that can be readily utilized by practicing engineers. Additionally, a comparison between the strut-and-tie method and standard sectional design practices will be performed for a typical hammerhead pier.

Influence of substructure design and spacer settings on the in vitro performance of molar zirconia crowns

Objectives The aim of this study was to evaluate the in vitro behaviour of all-ceramic zirconia molar crowns in regard to different core designs and marginal fit. Methods Identically shaped methacrylate molars were prepared according to the ceramic restoration directives resulting in a 1-mm deep circular shoulder preparation. They were embedded in polymethylmethacrylate resin after covering their roots with a polyether layer to simulate periodontal mobility. The crown cores were made of yttria-stabilized zirconia veneered with a corresponding veneering ceramic. The crowns were divided into 5 groups ( n = 8) which differed in core design and cement gap thickness: #1: simple core, 40 μm cement; #2: core with minimal occlusal support, 40 μm cement; #3: core with optimized cusp support, 40 μm cement; #4: core with optimized cusp support, 30 μm cement; #5: core with optimized cusp support, 10 μm cement. All crowns were cemented with zinc oxide phosphate cement and thermo mechanically loaded (1.2 × 10 6 × 50 N; 6000 × 5 °C/55 °C) with identical metal ceramic restorations as antagonists. Crown failures were monitored and described. Area and direction of the chipping failures of the veneering ceramic were documented by means of scanning electron micrographs. Results All core designs showed chipping during chewing simulation with different numbers (defect areas). #1: 6 chippings (8.1 mm 2); #2: 2 chippings (3.5 mm 2); #3: 2 chippings (2.1 mm 2); #4: 3 chippings (5.7 mm 2); #5: 3 chippings (7.3 mm 2). Conclusions An optimized core design reduced number and surface area of occurring chippings. A variation of the gap thickness showed no significant influence on the in vitro performance.

Structural optimization of the fibre-reinforced composite substructure in a three-unit dental bridge

Introduction Failures of fixed partial dentures (FPDs) made of fibre-reinforced composites (FRC) have been reported in many clinical and in vitro studies. The types of failure include debonding at the composite-tooth interface, delamination of the veneering material from the FRC substructure and fracture of the pontic. The design of the FRC substructure, i.e. the position and orientation of the fibres, will affect the fracture resistance of the FPD. Objectives The purpose of this study was to find an optimal arrangement of the FRC substructure, by means of structural optimization, which could minimize the failure-initiating stresses in a three-unit FPD. Methods A structural optimization method mimicking biological adaptive growth was developed for orthotropic materials such as FRC and incorporated into the finite element (FE) program ABAQUS. Using the program, optimization of the fibre positions and directions in a three-unit FPD was carried out, the aim being to align the fibre directions with those of the maximum principal stresses. The optimized design was then modeled and analyzed to verify the improvements in mechanical performance of the FPD. Results Results obtained from the optimization suggested that the fibres should be placed at the bottom of the pontic, forming a U-shape substructure that extended into the connectors linking the teeth and the pontic. FE analyses of the optimized design indicated stress reduction in both the veneering composite and at the interface between the veneer and the FRC substructure. Significance The optimized design obtained using FE-based structural optimization can potentially improve the fracture resistance of FPDs by reducing some of the failure-initiating stresses. Optimization methods can therefore be a useful tool to provide sound scientific guidelines for the design of FRC substructures in FPDs.

Deflectometer-based analysis of ballasted railway tracks

The falling weight deflectometer (FWD) device is used in the UK for the dynamic testing of ballasted railway track. Using the deflection data obtained from the test, elastic modulus values of the track substructure required to build a numerical model of the track can be determined using a procedure known as back-analysis. The numerical model so calibrated can be used to determine the effect of the traffic loads on the stresses, strains and deformations in the railway track system, and is an important component of an analytical approach to track substructure design. In this paper, the use of dynamic finite-element analysis to back-analyse the material properties of the railway substructure from FWD deflection data has been demonstrated by means of an example. The numerical approach presented is the rational method for FWD-based inverse analysis and condition evaluation of ballasted railway tracks, and becomes practicable owing to continued advances in finite-element and computer technologies.