Excessive Deflection Research Articles

Decreasing of vibration amplitudes of the converter pedestal by design changes and changes in prestress of the bolted joints

A new converter was installed on the pedestals on which the original converter sat. During the testing operation of the new converter there were found excessive deflections of the converter pedestals in locations of the bearing houses of the converter vessel. A detailed analysis based mainly on experiments showed the cause of these excessive vibrations of the converter pedestal. With proposal and implementation of design improvements in the location of bolt connections as well as changes both in anchoring of the pedestal and of the prestress in the bolts, the deflections were decreased below the allowed value.

Materials Challenges in Present and Future Wind Energy

AbstractThe main concept currently in use in wind energy involves horizontal-axis wind turbines with blades of fiber composite materials. This turbine concept is expected to remain as the major provider of wind power in the foreseeable future. However, turbine sizes are increasing, and installation offshore means that wind turbines will be exposed to more demanding environmental conditions. Many challenges are posed by the use of fiber composites in increasingly large blades and increasingly hostile environments. Among these are achieving adequate stiffness to prevent excessive blade deflection, preventing buckling failure, ensuring adequate fatigue life under variable wind loading combined with gravitational loading, and minimizing the occurrence and consequences of production defects. A major challenge is to develop cost-effective ways to ensure that production defects do not cause unacceptable reductions in equipment strength and lifetime, given that inspection of large wind power structures is often problematic.

콘크리트를 충진한 FRP 합성 거더의 파괴 거동에 관한 연구

This study is about manufacturing and producing girder, which is an essential component of bridge structure, in a composite of FRP + concrete. This has a higher competitive power in price than steel girder. The girder used in this study is made of glass fiber which has a lower elastic modulus than steel and thus has some technical limitations such as excessive deflection compared to steel girder and lack of production facilities in FRP production companies to make a large-section component material. Thus, this study suggested a section of a new module that will allow for applying a large section in order to solve the technical difficulties mentioned above and to secure low stiffness of FRP, developed a new FRP+concrete composite girder that is filled with the appropriate amount of concrete. To identify the structural behavior of this FRP+concrete composite girder, experiments were conducted to measure its flexural strength according to the difference in the strength of confined concrete and the existence of stud. The results of the flexural strength test confirmed the composite effect from confining concrete and the effect of increase in strength proportional to the strength of concrete. In developing FRP+concrete composite girder, NDT study was also conducted to analyze the interface characteristics of concrete and FRP.

Assessment of Strength Compliance with Standards for Tanzania Eucalyptus Wood Poles Treated with Copper-Chromium-Arsenic Compounds

Samples of copper-chromium arsenic compounds (CCA) treated Eucalyptus poles for power transmission were sampledfrom a lot following Military Standard MIL-STD 105D, Single sampling, Tightened Inspection, Acceptable Quality Level(AQL) of 4 as provided for in the South African Standard SABS 754:1994 from lots containing 151-500 poles. Sampleswere randomly selected from a lot. Maximum fiber stresses were evaluated taking into account the actual taper in eachpole. The cantilever loading test was performed on the samples following SABS 754:1994. It was found out that theaverage taper for the poles was smaller than that assumed in the standard due to the different pole growthcharacteristics and environment in Tanzania and that the average modulus of elasticity obtained for the poles was lowerthan the average assumed in SABS 754:1994. The poles also showed excessive deflections at working loads. It isrecommended to the Tanzania Bureau of Standards that although SABS 754:1994 is meant to be used for eucalyptuspoles grown in Southern Africa south of the Sahara that are treated with creosote or CCA there is a need to review it totake into account the actual characteristics of the poles grown in Tanzania where they are normally grown in highlandareas with higher rainfall and colder climates.

Analysis and design of partial ground improvement in deep excavations

Excessive wall deflection and ground settlement are common problems for deep excavations in soft clay and frequently damage adjacent buildings. To reduce wall deflection or ground settlement, the in situ soil is usually strengthened by jet grouting or mechanical deep mixing method. Finite element analysis can be conducted to determine improvement ratios, improved depths and improved zones of the soil to reach a balance between cost and safety. However, the conventional two dimensional finite element method does not take into account corner effects, which will affect the determination of improved zones. A three-dimensional finite element method is thus appropriate for analysis. In this study, an excavation 51.65 m long, 23.75 wide, and 9.31 m deep was used as an example to show how to design the improved zone using ideas of corner effects and the three-dimensional finite element method. It was found from a series of parametric studies that the lateral wall deflection was virtually not affected if the area within 8 m from the corners was or was not improved, which was subsequently used for the ground improvement in the actual excavation. The wall deflections were carefully observed during excavation. It was found that the measured wall deflections were close to those originally designed. The adjacent buildings near the excavation site were thus protected.

Case Study: Strengthening of Parking Garage Decks with Near-Surface-Mounted CFRP Bars

This paper describes a parking garage retrofitting project where near-surface-mounted carbon fiber-reinforced polymer (FRP) bars were used to strengthen the reinforced-concrete decks. The garage reportedly exhibited numerous signs of deterioration, such as excessive deflections of the decks at bay midspans, extensive concrete cracking, concrete spalling, etc. The results of the structural analyses indicated that several negative-moment slab regions were deficient to support the design loads. The amount of overstressing was up to 50% in some areas. The structural analysis considered as-built conditions and showed that deficiencies were predominantly due to misplacement of the negative-moment steel reinforcement. The paper summarizes the design approach for carbon FRP strengthening of the concrete decks and describes a load testing program used to evaluate their performance. Finally, a description of parameters and considerations used in development and implementation of the adopted strengthening strategy is also presented.

Field calibration of time-dependent behavior in segmental bridges using self-learning simulation

The construction of segmental bridges often shows unexpected deflections, mainly due to the complex time-dependent behavior of concrete. The control of excessive deflections is important for the successful completion of their construction. It is difficult to accurately predict these deflections purely by conventional numerical simulations, and often the preferred method is field calibration. The quality of the calibration is dependent on the experience of the engineers involved. Therefore, it is difficult to systematically quantify and benefit from the gained experience, and to accumulate it. We employ a novel method called Self-learning Simulation (SelfSim), which integrates numerical simulations and field observations. SelfSim “learns” the time-dependent behavior of concrete in the field from displacement measurements. The gained knowledge is retrieved using extracted stresses, strains, rates of stresses and strains, and a neural network-based constitutive model. SelfSim is able to provide predictions about the remaining or future construction with the gained knowledge. Deflections can be controlled systematically by using the information provided by SelfSim. As a demonstration, the proposed method is applied to the field calibration of the Pipiral Bridge, a concrete segmental bridge built by the balanced cantilever method.

Time-dependent analysis and simulation-based reliability assessment of suspended cables with rheological properties

The intention of the paper is to illustrate the ability of the probabilistic time-dependent reliability assessment procedure applied to non-linear suspended cable structure with rheological properties, when a rope made from the high strength synthetic fibres is used in order to demonstrate the new qualitatively different concept. Attention is turned to the individual main steps in the assessment procedure, i.e. to the selection of an appropriate method of structural analysis and to derivation of an appropriate closed-form and discrete analytical models, analysis of random variables representing individual actions (four basic random variables, such as structural geometry, cable’s modulus of elasticity and creep strain increments and loading, are considered), evaluation of the structural response with respect to the interaction of the random variables considering a history of the time-dependent action effects and to the definition of the limiting values considering serviceability of cable structure. The potential of the method using direct Monte Carlo technique as one of the possible alternatives for simulation-based time-dependent reliability assessment as a powerful tool is emphasized. The influence of an excessive deflection of suspended cable (caused by creep of cable and rheologic changes) on its serviceability in required time is investigated and illustrative examples are performed.

Moment Capacities and Deflection Limits of PFRP Sheet Piles

The structural response of pultruded fiber-reinforced polymer (PFRP) sheet pile panels subjected to a uniform pressure load was investigated. Single, connected, and concrete-backfilled panels were tested to ultimate failure in an attempt to determine their moment capacities, deflection limits, and failure mechanisms. The load-carrying capacity of single-panel FRP piles was found to be 15% higher than that of three panels connected together. No pin and eye joint separation was observed at failure. The concrete backfilled hybrid panels exhibited significantly increased moment capacity. However, the increase in stiffness after the first concrete crack was, at best, only 76% over the pile without backfill. Bearing failure of a PFRP pile with a partially confined support created excessive deflection in the wall, but showed no significant reduction in the load capacity. On the other hand, with fully confined support, the ultimate failure of single, connected, and concrete-backfilled panels was dominated by loca...

Investigation on the flexural behaviour of high-performance reinforced concrete beams using sandstone aggregates

In recent years, an emerging technology termed high-performance concrete (HPC) has become popular in construction industry. The constituent materials of HPC depend on the desired characteristics and the availability of suitable local economic alternatives. Tests are reported in this study on the flexural behaviour of high-performance reinforced concrete (HPRC) beams made with crushed sandstone coarse and fine aggregate together with silica fume. The beams were made from concrete having compressive strength of 74 and 78N/mm2 and tensile reinforcement ratio in the range of 1.34–3.14%. The ultimate moment for the tested beams was found to be about 14–30% and 3–9% higher than that of the predicted ultimate moment based on BS 8110 and ACI 318, respectively. Due to lower stiffness of sandstone aggregates, the beams resulted in excessive deflection under service loads. The observed crack width under service loads were within acceptable limits. The mineral fillers in crushed sandstone sand and silica fume increased the flexural stiffness of HPRC beams and resulted in adequate safety factors against flexural failure. The test results showed that it is possible to produce HPC using sandstone aggregates with silica fume and superplasticisers.

Deflection control of elastically restrained laminated frames under deterministic and uncertain loads using induced strain actuators

Optimal induced strain actuator sizes for an L-shaped laminated frame are determined under deterministic and uncertain loads with the objective of minimizing the tip deflection. The bending moments generated by the induced strain actuators control the deflection in order to minimize the maximum deflection. The frame is elastically restrained at the tip point and is subjected to a tip load which is specified for the deterministic case and lies in an uncertainty domain in the uncertain case. The specific uncertain loading studied in the present paper involves a load of given magnitude but of unknown direction which should be determined to induce the highest tip deflection caused by the least favorable loading. The effects of the elastic restraints and actuator locations on the deflection behaviour are investigated. It is shown that the optimal actuator size depends on the magnitude of the moments provided by the actuators. Moreover, it is observed that a deterministic design under an uncertain load leads to excessive deflections indicating the necessity of a robust design.

Energy Capacity Criterion for the Design of Columns against Collapse

Current practice in buckling design is based on the ultimate strength of a member such that excessive lateral deflections do not occur. This ultimate strength is often dictated by empirically derived formulae which correspond to postulated element imperfections including residual stresses. In this paper, the postbuckling behavior of columns is considered, and the limit state is considered to be total collapse. The load versus end displacement relationship is derived for a simplified elastic–perfectly plastic column model. Using this curve, the energy absorbed and released in going from one load/deflection state to another can be easily quantified. With this, the energy absorption capacity of an already loaded column is considered to be the critical performance metric. This “energy capacity criterion” is then used to develop alternative design curves for different levels of energy absorption capacity.

유리와 탄소섬유로 제작된 하이브리드 FRP 로드의 인장특성에 관한 실험연구

Recently, Fiber Reinforced Polymers(FRP) has been emerged as an alternative material to solve the corrosion of steel reinforcement in reinforced concrete structures. FRP exhibits higher specific strength and lower weight compared to steel reinforcement. Moreover, good resistance to corrosion of the FRP may be useful in aggressive environments causing deterioration such as chloride environment. However, causes for higher initial cost of FRP than that of steel, little information on the long-term behavior of FRP, and brittle failure make the efforts to apply FRP in civil structures slow. Glass fiber among the fibers used to manufacture FRP can be seen as the most beneficial material with regard to initial costs. But its low elastic modulus, which attains barely a quarter of steel, nay thus lead to excessive deflections when used as reinforcement for flexural members. This research was carried out on the tensile properties of hybrid rods made with glass and carbon fibers to improve those of FRP rod made with glass fiber. Parameters were resin type and the arrangement of glass and carbon fibers. The tensile properties of hybrid rods were compared with those of rods manufactured with only glass or carbon fibers. The results indicated that the tensile properties of hybrid rod were good when the carbon fiber was arranged in the core.

Time-Dependent Reliability Method to Assess the Serviceability of Corrosion-Affected Concrete Structures

Corrosion induced structural failures do not necessarily imply structural collapse but in most cases are manifested by loss of structural serviceability, characterized by concrete cracking and the excessive deflection. This paper attempts to develop a performance-based methodology for serviceability assessment of corrosion affected concrete structures. Methods of time-dependent reliability are employed to quantify the probability of serviceability failure. A merit of the developed methodology is that the structural response is directly related to design criteria used by structural engineers and asset managers. It is found in the paper that, under the same service conditions, corrosion induced cracking attains a serviceability limit state before deflection does. It is concluded that a time-dependent reliability method can serve as a tool for structural engineers and asset managers to develop a risk-informed and cost-effective strategy in the management of corrosion-affected concrete structures.

Modelling crimp in woven fabrics subjected to ballistic impact

Woven fabrics are widely used in flexible armour systems for protection against fragments and projectiles from small arms. The woven architecture introduces crimp or undulations in the yarns as they pass alternately over and under orthogonal yarns. An undesirable effect of crimp is excessive deflection in fabric armour during impact. The numerical results of ballistic impact and perforation of woven aramid fabric are presented in this paper. The fabric is modelled as a network of nodal masses connected by one-dimensional viscoelastic elements. The focus of the computational simulation is to compare two different ways of incorporating yarn crimp into the fabric model. Tensile tests on strips of the woven fabric show an initial toe region in the load–deflection curve before the curve asymptotically converges to an approximately straight line beyond a certain strain. The first method of introducing crimp into the fabric model is to include the toe region of the load–deflection curve in the constitutive equation describing the viscoelastic elements. The second method to account for crimp is to physically reflect the woven architecture in the fabric model by arranging the chain of linear elements that define each yarn in a zigzag manner.

A Novel Automatic Feedrate Adjustment Method for Die-Cavity Roughing

Sculptured surface machining is a critical process commonly used in die and mold industries. Since there is a lack of scientific tools in practical process planning stages, feedrates of CNC machining are selected based on previous experiences. In the selection of feedrate, the feedrate is set an individual conservative constant value all along the die cavity roughing processes in order to avoid undesirable results such as chipping, cutter breakage or over-cut due to excessive cutter deflection. Usually, volumetric models or vector force models used for optimizaton of feedrates must be created to get the variable feedrates along the tool path. Considering the die cavity roughing being a 2.5D cutting, a novel cutting force surface model is created based on orthogonal cutting tests to adjust the feedrates. The model is tested by a typical die-cavity roughing, thinning down machining time and balanced cutting-load can be attained. The presented feedrate scheduling characterized by balancing the cutting-loads in die-cavity roughing will be more significative in high speed machining.

프리스트레스트 이중 콘크리트 보의 휨 거동 해석

Cracks due to low tensile strength in prestressed concrete (PC) beams may decrease rigidity and structural performance, resulting in excessive deflection. In an effort to solve this problem, in this research, prestressed dual concrete (PDC) has been proposed, consisting of normal strength concrete in compression zone, and high performance steel fiber reinforced concrete(HPSFRC) with a partial depth in tensile zone. Three PDC beams with different depths of HPSFRC and two PC beams were cast for experiments. Analytical models at each stage, i.e., precracking, postcracking, and ultimate, were proposed for analysis of flexural behavior in PDC beams. The experimental results agree well to the analytical ones. Crack formation and its propagation are controlled by the HPSFRC in PDC beams. The initial cracking and service limit loads are increased along with the load carrying capacity and flexural stiffness.

Metal sandwich plates optimized for pressure impulses

Survival of a plate against an intense, short duration impulsive loading requires the circumvention of failure modes, including those associated with excessive overall deflection and shear-off at supports and webs. All-metal sandwich plates have distinct advantages over comparable weight monolithic plates, especially for intense water loadings. A recently developed mechanics of dynamically loaded sandwich plates by N. A. Fleck and V. S. Deshpande is extended and modified to address the problem of the minimum weight design of plates of given span that must sustain a uniformly distributed impulsive wave in air or water environments. Requirements for core crushing strength and energy absorption are discussed, as are conditions governing shear-off of the face sheet. Dimensionless parameters governing optimal designs are identified. Specific results are presented for plates with square honeycomb cores outlining trends for the best performance that can be achieved and the optimal distribution of mass between faces and core. Optimally designed sandwich plates can sustain water shocks that are two to three times as large monolithic plates of the same mass and material. The model is used to discuss a number of issues relevant to the design of effective metal sandwich plates, including differing requirements for air and water environments, face sheet shear-off resistance, the role of core strength, and the relation between small-scale tests and full-scale behavior.

Structural Modeling of Profiled Edge Laminae (PEL) Tools

Profiled Edge Laminae (PEL) tooling is a thick-layer Rapid Tooling (RT) method that involves assembling an array of laminae—each having a uniquely profiled and beveled top edge—together in a precise and repeatable manner by registering each lamina’s bottom edge and an adjacent side edge to a fixture that has precisely machined edges. The processed laminae are then clamped or bonded into a rigid tool for use in manufacturing (e.g., as a thermoforming mold). Because a PEL tool is inherently more compliant than a solid tool, manufacturing personnel who are considering its use are understandably concerned about excessive tool deflection, which may lead to unacceptable changes in tool shape, decreased tool life due to high stresses and increased wear, and part dimensional errors. The ability to predict deflection (i.e., shape changes) in a laminated construction, either clamped or bonded, is extremely important to promote widespread acceptance of the PEL method. This paper develops basic analytical structural models for both clamped and adhesively bonded PEL tools, which will allow tooling designers and engineers to predict how changing various design parameters (e.g., the number of laminations, tool material, unclamped length of laminations, bonding adhesive, adhesive thickness) affect a tool’s stiffness. Deflection results from these models are shown to agree very well with experimental results. The usefulness of these analytical models is then shown by a design example. Finally, FEM modeling of PEL tools is demonstrated and shown to provide results that agree reasonably well with experimental results. FEM modeling may allow for prediction of shape changes to a PEL tool characterized by a complex three-dimensional surface and subject to arbitrary structural loads.

Field Performance of High Density Polyethylene Culvert Pipe

The effect of installation procedures on the field performance of existing high density polyethylene (HDPE) pipe used for drainage applications on highway projects was investigated. A total of 45 HDPE pipes were inspected at sites in South Carolina that were statistically selected based on geographical location, pipe diameter, use, and age. The condition of each pipe was not known prior to selection for inspection. Both the external and internal conditions of the pipe were evaluated with respect to AASHTO and ASTM specifications, measurements of pipe deflection with a mandrel set to 5% deflection, and visual inspections of the pipe interior using a video camera. The video camera inspections revealed circumferential cracks in 18% of the pipes, localized bulges in 20% of the pipes, and tears or punctures in 7% of the pipes. Deflections greater than 5% were observed in 20% of the pipes. Installation problems such as poor preparation of bedding soils, inappropriate backfill material, and inadequate backfill cover contributed to the excessive deflection and observed internal cracking in pipes with observed damage. Appropriate construction procedures are essential in achieving a proper installation.