Differential Deflection Research Articles

Analysis, design & installation of vibration isolation for lightweight helipads: a case study

The heliport isolation aims to mitigate the transmission of helicopter-induced vibrations to the building structure during approach, landing, and take-off by introducing vibration isolators at the supports of the heliport structure. As a case study, this paper presents the design and manufacturing steps for the installation of a vibration isolation solution for two lightweight helidecks installed on the rooftop of an existing medical center building. Design of a very high-performance isolation system for a lightweight helideck, requires a series of stability checks under various load conditions. In practice, the primary challenge is to control the substantial differential deflection of the helideck, which is supported by relatively soft isolators, during approach and landing conditions. The solution delivered was a prefabricated spring box comprising essential components such as failsafe and uplift restraints to deal with the challenging aspects of the isolation of lightweight helidecks. Certainly, a collaborative effort between the isolation solution provider and the helideck supplier facilitated a progressive design process aimed at meeting stringent acoustic performance requirements and addressing the complex functionality of a lightweight helideck. The paper also discusses the challenges and best practices encountered during the production and installation of the system.

Performance Improvement of Winged Compound Helicopter Due to Differential Flap Deflections

A lift-offset system for a single-rotor-type compound helicopter is proposed to improve the aerodynamic performance in high-speed flight. The proposed system utilizes the differential flap deflections on the fixed wings to produce a rolling moment, which is counteracted by the single main rotor, causing the rotor to operate in a lift-offset state. The performance of the proposed system is evaluated through numerical simulations. At first, the effect of lift offset with regard to lift-share ratio on the rotor performance is investigated. Then, the impact of lift offset due to the differential flaps on the overall effective lift-to-drag ratio is studied. The results show that the lift offset significantly improves the rotor performance and the overall effective lift-to-drag ratios, especially at larger rotor lift-share ratios. The overall effective lift-to-drag ratio increases by 10% due to the differential flaps compared to the zero-flap deflections. It is concluded that the lift offset due to the differential flaps achieves more efficient cruising flight for a single-rotor-type compound helicopter.

Controlling roll-yaw coupling with aileron and twist design

AbstractMost simple ailerons produce adverse yaw. However, with proper aileron placement and wing twist, an aileron can produce proverse or neutral yaw, eliminating the need for aileron-rudder mixing, differential aileron deflection or Frise ailerons. The relationship between wing planform, aileron placement and lift distribution is studied here for a special class of optimal lift distributions that minimise induced drag for a variety of design constraints. It is shown that a wing employing the elliptic lift distribution will always produce adverse yaw, independent of aileron design or operating condition. However, for wings employing other optimal lift distributions, the ailerons can be placed to produce proverse or neutral yaw. A numerical lifting-line algorithm is used to explore the impact of aileron design on a wide range of wing planforms and lift distributions. Results can be used in the early stages of design to correctly place ailerons with respect to desired roll-yaw coupling.

A laboratory investigation and numerical modeling on fiber reinforced lime and alkaline binder stabilized pavement subgrade soil

The differential settlement and excessive deflection in expansive subgrade soils lead to low volumetric stability upon moisture imbalance and cause severe damage to highway and airport field pavement surfaces. The present paper attempts to strengthen the stability behavior of expansive subgrade soil using an envirosafe alkaline binder (AB) with polypropylene fiber (PLF). AB was produced by combining dry aluminosilicate precursors (steel slag [SS] and sugarcane bagasse ash [SBA]) with a liquid activator (mixture of sodium hydroxide [NaOH] and sodium silicate [Na2SiO3]) in 0.4 water to binder (w/b) ratio. California bearing ratio (CBR) based resilient modulus, shear strength ratio (Sr), and consolidation tests were conducted as performance indicators of expansive subgrade soil reinforced with discrete PLF (0–0.5%) in 6% lime and 6% alkaline binder. The study also proposes the optimal sugarcane bagasse ash-steel slag-PLF dosage in the AB-stabilized subgrade layer. Moreover, mineralogical and morphological studies using powder X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) were also carried out to understand the crystalline compounds and micro surface texture of the soil-fiber mixture. It was revealed that AB-fiber-soil exhibits higher interfacial frictional bonding and interlocking density than lime-fiber-soil. Also, 2D finite element analyses were carried out to compare the behavior of subgrade under the influence of vehicular load on the surface. PLF-AB soil mixture shows 72% lower vertical deformation than unstabilized expansive soil. Based on the findings of this study, recommendations for the practical application of stabilizing expansive subgrade soils were proposed.

Behavior of Stiffened Rafts Resting on Expansive Soil and Subjected to Column Loads of Lightweight-Reinforced Concrete Structures

An approach to estimate the behavior of stiffened rafts under column loads of a lightweight-reinforced concrete structure resting on expansive soils is presented in this paper. The analysis was conducted using the computer program SLAB97, which estimates the 3D distorted mound shape using the finite difference method by solving the transient suction diffusion equation in 3D and computing the corresponding soil movements. The interaction between the stiffened rafts and the 3D distorted mound shape is then analyzed using the finite element method. The SLAB97 program has been validated by comparing its results with the results of others that were shown to be valid. The goal of the study is to make the expansive soil structure interaction models that the previous researchers proposed more logical. Assuming the worst initial 3D distorted mound shapes of the two cases of edge heave and edge shrinkage, an upper-bound solution is obtained. Using the two scenarios of edge shrinkage and edge heave, the program was utilized in a parametric investigation to examine the impact of various parameters on the behavior of stiffened rafts on expansive soils. These parameters include the stiffening beam depth, the maximum differential movement of the distortion mound shape, and the raft dimensions. The behavior of the stiffened rafts subjected to concentrated column loads is concluded to be similar to that of the stiffened rafts subjected to uniform and perimeter line loads in both cases of distortion modes, with regard to the shape of raft deformation and distribution of the bending moments; however, the values of the design parameters such as maximum deflection, maximum differential deflection, and maximum moments are entirely different in these two situations.

Empirical fragility and ROC curves for masonry buildings subjected to settlements

In the Netherlands, the potential damage to the building stock due to subsidence phenomena has recently received increased awareness. However, evaluating and predicting damage to buildings in subsiding areas is a complex task that requires associating the vulnerability of exposed structures with the intensity of the subsidence hazard. Considering the widespread presence of subsidence-related damage to the built heritage, the focus of this study is to provide empirical-based insights to assess and forecast subsidence damage to masonry buildings. A rich dataset with manual levelling measurements was collected comprising 386 surveyed masonry buildings, mainly low-rise (terraced) houses built before 1950. Of the total set of buildings, 122 cases rest on shallow foundations and 264 on piled foundations. For each building, the recorded damage is related to the settlement, calculated from the bed-joint levelling measurements, using four different intensity parameters, namely differential settlement, rotation, relative rotation and deflection ratio. These four parameters are appraised in their capacity to effectively predict the intensity of the damage. The Receiver Operating Characteristic (ROC) method is used to evaluate the relative efficacy of the selected hazard parameters. The rotation, the relative rotation (angular distortion) and the deflection ratio are observed as the most accurate when predicting the intensity of damage, while the differential settlement appears less accurate.Additionally, the dataset was used to generate empirical fragility curves where the probability of damage is described as a function of the aforementioned parameters. Thresholds were set to distinguish between the light damage and the functional and structural damage state. At a relative rotation of 1/500 masonry buildings on shallow foundations were observed to reach or exceed light damage with a probability of 13%, and functional and structural damage with 5%. The availability of the bed joint levelling measurements made it possible to classify eight recurrent settlement profiles, including both symmetric and asymmetric profiles, associated with both the overall deformation and the rigid rotations of the surveyed buildings.

Numerical investigation of rigidity and flexibility parameters effect on superstructure foundation behavior using three-dimensional finite element method

A comprehensive three-dimensional finite element of the superstructure foundation model includes the effect of lots of important parameters on the structure performance. Among these parameters, rigidity and flexibility of raft foundations and soil interactions become an important aspect of design due to their efficient, practical and economic performance compared to the isolated foundation for buildings and heavy projects. In this study, the elastoplastic constitutive model based on the three-dimensional finite element (FE) method is employed to investigate rigidity and flexibility parameters' effect on superstructure foundation behavior. The model is developed and calibrated using SAFE 12 and ABAQUS programs by comparing two case studies. Utilizing the Winkler approach, flexible soil foundations are designed. In addition, technics like turning the raft into a boxed-raft or piled raft are evaluated to improve the performance of the raft from a rigidity and flexibility point of view. Then, the effects of various factors and conditions which affect design such as geometry, modulus of subgrade reaction, stiffness of the foundation, the effect of soil and thickness of foundation, piled raft foundations (PRF) and boxed raft foundations are studied. The results demonstrate that the superstructure components such as shear walls and basement walls can significantly affect the deflection, shear stress, and bending moment of the raft and its structural design subsequently. Also, shear walls, as structural parts which transmit an important part of vertical and lateral loads to the foundation, can play an important role in the rigidity of the raft. It is concluded that using PRF instead of the simple raft, results in a much rigid foundation with more bearing capacity and less differential deflection. The results of this study have the potential to be utilized in the design of advanced superstructure, in which rigidity and flexibility act as the basic elements.

Effect of Soil Stiffness on the Design Parameters of Stiffened Raft Foundation on a Highly Expansive Soil

This paper evaluates the effect of soil stiffness on the design parameters of a stiffened raft on an expansive soil of high potential for swelling. The evaluation was based on a finite element program originally developed by Wray [8]. The input soil parameters were measured in the laboratory for a highly expansive soil from Central Sudan. Soil Young’s Modulus was measured at varying moisture conditions using the unconfined compression test. The effects of soil modulus on moments, shear forces and differential deflection were investigated for a case study of a light residential building founded on the tested soil. Evaluation was made using different values of measured and assumed heave and end penetration. Results showed that the modulus of elasticity decreased as water content of the soil increased. The determined results of the finite element program suggested that, generally, the magnitude of longitudinal, traverse moments, shear forces, and differential deflection increased with increase in the soil modulus of elasticity and that the heave values affected the results.

Prediction of Residential Slab Foundation Movement Through a Finite Element-Based Deep Learning Algorithm

Deep learning networks were employed to predict the maximum differential deflection of stiffened and waffle rafts due to reactive soil movements, Δmax. Four deep learning networks were used to predict Δmax, these are (1) stiffened rafts on shrinking soil, (2) stiffened rafts on swelling soil, (3) waffle rafts on shrinking soil, and (4) waffle rafts on swelling soil. The deep learning models were used to create design lines, which showed that both soil and structural features strongly influence the stiffened rafts. In contrast, waffle rafts showed a strong dependence on soil features in shrinking soils and beam depth in swelling soils. This demonstrates that the finite element-based deep learning networks captured the effect of the embedment of the beams. The results of the deep learning models led to non-linear design curves, which are disparate from the suggested standard Australian design. These results suggest that increasing the value of beam depth can have a positive or negative impact on the global residential slab depending on the type of substructure and whether the founding reactive soil is shrinking or swelling. Global sensitivity analyses of the deep learning models showed that for stiffened rafts on shrinking soil, the slab length, slab width and active depth zone of reactive soil had the most significant influence on Δmax, whilst for stiffened rafts on swelling soil, the primary drivers are ground movement, beam depth, and slab width. The prediction of Δmax for waffle rafts on shrinking soil was driven by the surface characteristic and mound movements, and the active depth zone, whilst waffle rafts on swelling soil was driven by the beam depth. Overall, the finite element-based deep learning showed the capacity to estimate Δmax in both shrinking and swelling design scenarios for different types of residential footing systems to further understand the characteristic behaviour of shallow residential slab foundations on reactive soils leading to improved designs.

Two-dimensional measurement of resonance in MEMS resonators using stroboscopic differential interference contrast microscopy.

We report the two-dimensional (2D) measurement of resonance in MEMS resonators using stroboscopic differential interference contrast (DIC) microscopy, for the investigation of the linear and nonlinear oscillations of MEMS resonators. The DIC microscopy measures the interference of two sheared illumination light beams reflected from the sample surface to determine the differential surface deflection. By modulating the illumination light at the resonance frequency, the DIC image of the MEMS resonator periodically change its brightness and contrast with the sweeping illumination phase, which have been used to derive the oscillation amplitude and the resonance mode shape of the MEMS resonator. Comparing with conventional interference microscopy, the DIC microscopy can observe the surface deflection larger than the wavelength of the illumination light, enabling the measurement of nonlinear oscillations with a large oscillation amplitude. We demonstrate that the stroboscopic DIC microscopy can measure the 2D mechanical resonance with a high vertical resolution at the nanometer(nm)-scale, and a large measurement range of ∼1µm, which is very promising for the investigation of linear and nonlinear oscillations of MEMS resonators.

Deformation Response and Safety Evaluation of Buildings Affected by Subway-Station Construction

Based on the sand and pebble stratum in the Beijing area, this paper studies the interaction between deep-foundation-pit excavation for subway stations and surrounding buildings using an orthogonal test. Moreover, it considers the relative position relationship between buildings and how the foundation pit is set up as well as different design schemes for foundation pits and the surrounding buildings. Results show that the horizontal distance s between the building and foundation pit and stiffness of the building itself have a clear impact on the differential settlement δij and relative deflection Δ, and the degree of deformation of the building near the corner of the foundation pit is complex. Simultaneously, based on numerical simulation results, the deformation characteristics and degree of deformation of the building under different relative position relationships with the foundation pit are analyzed. Finally, by establishing a relationship among the comprehensive deformation index Dj, surrounding environmental safety evaluation index Sj, and scheme safety grade Lj, a multiangle safety evaluation method for buildings affected by foundation-pit construction is formed, which can provide a reference for the research and design of similar projects.

Exterior girder rotation of skew and non-skew bridges during construction

In bridge design, bridge decks regularly overhang past the exterior girders in arrange to extend the width of the deck whereas constraining the specified number of girders. The overhanging part of the deck comes about in uneven eccentric loads to the exterior girders which are by and large most prominent. These eccentric loads are primarily a result of bridge construction operations as well as the weight of new concrete and other construction live loads. These unbalanced loads can lead to a differential edge deflection of overhang deck and a rotation of the exterior girders. The girder rotation or differential deck deflection can also affect local and global stability of the entire bridge. The objective of this study is to enhance the knowledge and understanding of external girder behavior due to unbalanced eccentric construction loads and to identify the critical factors affecting their rotation. In this article, field data obtained during the construction of two skewed (one with a small skew (3.8°) and the second with a severe skew (24°)) and one non-skewed steel girder bridges are described, and a detailed comparison is presented. The three bridges experienced maximum outward exterior girder rotation during construction which subsequently decreased following construction operations. The field results were used to validate and calibrate the finite element models. The numerical and field-monitored data showed good agreement and can be used to assist bridge designers and construction engineers to design appropriate systems to limit girder rotation during construction.

Settlement analysis of pile cap with normal and under-reamed piles

The use of pile foundations has become more popular in recent years, as the combined action of the pile cap and the piles can increase the bearing capacity, reduce settlement, and the piles can be arranged so as to reduce differential deflection in the pile cap. Piles are relatively long, slender members that transmit foundation loads through soil strata of low bearing capacity to deeper soil or rock strata having a high bearing capacity. In this study analysis of pile cap with considering different parameters like depth of the pile cap, width and breadth of the pile cap, type of piles and different types of soil which affect the behaviour of pile cap foundation is carried out by using Finite Element Software ANSYS. For understanding the settlement behaviour of pile cap foundation, parametric studies have been carried out in four types of clay by varying pile cap dimensions with two types of piles namely normal and under-reamed piles for different group of piles. Furthermore, the analysis results of settlement and stress values for the pile cap with normal and under-reamed piles are compared. From the study it can be concluded that settlement values of pile cap with under-reamed pile are less than the settlements of pile cap with normal pile. It means that the ultimate load bearing capacity of pile cap with under-reamed piles are greater than the pile cap with normal piles.

Lateral Behavior Analysis due to Differential Deflection between Jetty Structures

Ji, H.W.; Kim, H.J., and Park, K.Y., 2020. Lateral behavior analysis due to differential deflection between jetty structures In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1–5. Coconut Creek (Florida), ISSN 0749-0208.Particular attention shall be paid to the design of steel/concrete structures supporting piping or equipment which have a sensitiveness to deflection. In case of excessive displacement generated in the substructure, the supported topside facilities can be subjected to additional stress caused by the imposed-deformation. Therefore differential deflection between structures should be estimated and then to be considered in the topside facilities. However, it is incredibly difficult for designer to predict the lateral behavior of the structures, using existing simple ways, under environmental and seismic load. Therefore a rigorous analysis should be performed to investigate the lateral behavior of the structures.

Analytical design of control system mathematical models for mobile robots based on the methods of inverse problems of dynamics and modal PID controllers

Mathematical models of a three-wheeled mobile robot based on the variable state apparatus and in the operator’s form are presented. Based on these mathematical models, the synthesis of its adaptive control system is carried out according to the method of constructing Ziegler-Nichols PID controllers, as well as modal PID controllers. The design method of proportional controllers with double differentiation (PDD) of the autonomous robot is justified. The rules of wheel pair control are synthesized on the basis of reference models using a simple gradient scheme of the inverse problems method of dynamics in the formulation of P. D. Krutko for the problem of stabilizing (blanking) the angular velocities for a three-wheeled mobile robot. Simulink-models of robot movement are developed for cases with the use of PID-controllers which are adjusted by the Ziegler-Nichols method at synchronous deviation of wheels. Simulink-models of robot motion have been developed for cases using PID controllers set up according to the Ziegler-Nichols method for synchronous wheel deflection, modal and real PID controllers for differential wheel deflection, as well as double differentiation controllers. The analysis of modeling results is considered.

Evaluation and upgrading web-gap distortion retrofits in steel girder bridges

Distortion-induced fatigue cracking in the unstiffened web-gap of cross-frame diaphragms is the most prevalent type of cracking in steel girder bridges. Multi-steel girder bridges experience differential deflection between adjacent girders when subject to vertical loads resulting in a driving force in cross-frame diaphragms. The driving force developed in the cross-frame legs leads to out-of-plane distortion of the web-gap which results in high stress concentrations at the area, following by fatigue damages. This paper introduces an innovative method to retrofit web-gap distortion cracking, upgrade existing retrofits, and compare its effectiveness with two common retrofit techniques. The method involves cutting the existing connection plate and using angles to attach the disconnected part of the connection plate to the web. The method intends to eliminate the local high stresses at the connection plate end with considering minimal interference in original connection design and load path. Also, two other conventional repair methods were investigated, slot method and top-angle measure, to use as a basis for comparing the methods effectiveness. Laboratory testing was performed on a small-scale steel bridge bay by applying a vertical displacement to the free end of a cross-frame diaphragm to simulate the differential deflection between two adjacent girders in real bridges. The results from the testing were compared to findings from finite element analyses (FEA). Test results as well as FEA results for all investigated retrofit techniques are presented herein. Results showed that the newly developed slot-angle technique has significant potential for effectively reducing the stress concentrations in the web-gap region by removing the location of initial stress concentrations and redistributing those stresses over a wider area.

Microcantilever aptasensor for detecting epithelial tumor marker Mucin 1 and diagnosing human breast carcinoma MCF-7 cells

In this paper, a simple and novel method based on microcantilever for detecting tumor biomarker MUC1 and diagnosing human breast carcinoma MCF-7 cells was proposed. With thiolated aptamers of MUC1 self-assembled on the sensing microcantilever, the targets interact with aptamers resulting in the change of surface stress on the microcantilever. As a result, MUC1 and MCF-7 cells were successfully detected. Among them, the differential deflection of the microcantilever is linear with the logarithm of the MUC1 concentration in the range of 5–500 nM with low detection limit of 0.9 nM. However, for MCF-7 cells, the linear relationship between cantilever deflection and cell concentration ranges from 2.0*103 to 5.4*104 cells/mL with low detection limits of 213 cells/mL. In the meantime, according to the characteristics of real-time recording the change of microcantilever deflection over time, we have speculated the dynamic process of the binding of MUC1 to the aptamers. This work has confirmed that the aforementioned microcantilever aptasensor could sensitively detect other biomarkers and provide dynamic information of binding, and also could be used to identify tumor cells.

INCREASE OF CONTROL SURFACES EFFICIENCY OF A SUBSONIC AIRCRAFT OF SHORT TAKEOFF AND LANDING

A steady growth of aviation transportation (4-5% per year) causes excessive saturation at numerous major airports. As a result, many flights are delayed. One of the ways to deal with this growing problem is to transfer regional propeller aircraft maintenance to suburban airports. It will require both a modernization of local airports and the design of a new generation of regional aircraft with short takeoff and landing (STOL). The aircraft ability to operate from short runways depends not only on wing unit loading and on high-lift capacities but also it is determined by the control surfaces efficiency. The latter often becomes one of the major reasons for limitation of the amount of lift used in STOL configuration. Thus, the successful application of high-lift devices stipulates the necessity for both the efficiency increasing of existing aircraft control surfaces and the development of some alternative form of lateral control not requiring a significant wingspan proportion. The forms of a lateral control, this article considers, include the interceptor, drooped ailerons, ailerons fitted with mini-flap and one of the alternative forms which uses differential flap section deflection. Several mini-flaps with a various chord are also considered to increase the available rudder yawing moment. The efficiency of the above-mentioned control surfaces has been studied in TsAGI low speed wind tunnel on a model of a twin-engine light aircraft with an enhanced level of lifting capacity on take-off and landing configurations. The tests were conducted at a Reynolds number of 1.0×10 6 and Mach number of 0.15.

ASSESSING THE CONDITION OF BURIED PIPE USING GROUND PENETRATING RADAR (GPR)

Abstract. The invention of Ground Penetrating Radar (GPR) technology has facilitated the possibility of detecting buried utilities and has been used primarily in civil engineering for detecting structural defects, such as voids and cavities in road pavements, slabs and bridge decks, but has not been used to assess the condition of buried pipes. Pipe deterioration can be defined as pipes where, for example, cracking, differential deflection, missing bricks, collapses, holes, fractures and corrosion exists. Assessing the deterioration of underground pipes is important for service efficiency and asset management. This paper describes a research project that focused on the use of GPR for assessing the condition of buried pipes. The research involved the construction of a suitable GPR test facility in the laboratory to conduct controlled testing in a dry sand. Plastic pipes were chosen for the experiments. A series of laboratory experiments were conducted to determine the validity and effectiveness of standard commercially available GPR technology in assessing the condition of buried utilities with common types of damage. Several types of damage to the plastic pipe were investigated with respect to different GPR antenna frequencies. The GPR surveys were carried out in order to obtain signal signatures from damaged and undamaged pipes buried at 0.5 m depth. These surveys were organised on a grid pattern across the surface of the sand in the test facility. The results presented in this paper show that GPR can identify certain types of damage associated with a buried pipe under these controlled laboratory conditions.

Application of polymer grids for reinforcement of asphalt pavement roads: Case study of corridor X in Macedonia

Asphalt paved roads prematurely exhibit a cracking pattern similar to that in the old underlying pavement. The cracking in the new overlay surface is due to the inability of the overlay to withstand shear and tensile stresses created by movements concentrated around preexisting cracks in the underlying pavement. This movement may be due to traffic loading causing differential deflections at cracks in the underlying pavement layers, expansion or contraction of subgrade soils, expansion or contraction of the pavement itself due to changes in temperature, or combinations of these phenomena. Due to heavy deformation of asphalt paved surface, using European funds, the Government of Macedonia initiated rehabilitation of Corridor X close to the Tetovo section. For the reconstruction of this important section of the motorway, an experimental programme was conducted to determine the effects of geogrid reinforcement on mitigating reflection cracking in asphalt overlays. The objective of this study is to assess the inclusion of geogrid in the pavement cross-section and the accumulation of permanent deformation. The geogrid position, type of existing pavement, temperature, and joint/crack opening were analyzed in three site trial tests. Crack propagation under repeated loading was monitored as well. The results indicate a significant reduction in the rate of crack propagation in reinforced samples compared to unreinforced samples of old asphalt pavement. The presented pavement design procedure could be tailored to the specific needs of the project and implemented in various road rehabilitation projects.