Vertical-to-horizontal response spectral ratio for offshore ground motions:Analysis and simplified design equation

In order to study the differences in vertical component between onshore and offshore motions,the vertical-to-horizontal peak ground acceleration ratio(V/H PGA ratio) and vertical-to-horizontal response spectral ratio(V/H) were investigated using the ground motion recordings from the K-NET network and the seafloor earthquake measuring system(SEMS).The results indicate that the vertical component of offshore motions is lower than that of onshore motions.The V/H PGA ratio of acceleration time histories at offshore stations is about 50%of the ratio at onshore stations.The V/H for offshore ground motions is lower than that for onshore motions,especially for periods less than 0.8 s.Furthermore,based on the results in statistical analysis for offshore recordings in the K-NET,the simplified V/H design equations for offshore motions in minor and moderate earthquakes are proposed for seismic analysis of offshore structures.

Towards establishing practical multi-hazard bridge design limit states

In the U.S., the current Load and Resistance Factor Design （LRFD） Specifications for highway bridges is a reliability-based formulation that considers failure probabilities of bridge components due to the actions of typical dead load and frequent vehicular loads. Various extreme load effects, such as earthquake and vessel collision, are on the same reliability-based platform. Since these extreme loads are time variables, combining them with not considered frequent. non- extreme loads is a significant challenge. The number of design limit state equations based on these failure probabilities can be unrealistically large and unnecessary from the view point of practical applications. Based on the opinion of AASHTO State Bridge Engineers, many load combinations are insignificant in their states. This paper describes the formulation of a criterion to include only the necessary load combinations to establish the design limit states. This criterion is established by examining the total failure probabilities for all possible time-invariant and time varying load combinations and breaking them down into partial terms. Then, important load combinations can be readily determined quantitatively,

Responses of wind-induced internal pressure in a two-compartment building with a dominant opening and background porosity Part 2:Parameter analyses and design equations

Analyses of the effects of some parameters were performed to determine the admittance functions in a common two-compartment building with background porosity by the imposed excitation method.Variations of the magnification factors of fluctuating internal pressures were analyzed using 96 model cases under random fluctuating external pressure,and then corresponding design equations were fitted.The results show that the Helmholtz resonance peaks of the admittance functions in both compartments increase with increasing the area of windward or partition wall opening.With increasing the volume of the compartment with an external opening,the resonance peak in this compartment at the higher Helmholtz frequency significantly decreases,at the same time,the resonance peak in the other compartment at the lower Helmholtz frequency also decreases.With increasing the volume of the compartment with background porosity,both resonance peaks in this compartment at the lower and higher Helmholtz frequencies decrease,meanwhile,the resonance peak at the lower Helmholtz frequency for the other compartment also decreases,whereas the resonance peak at the higher Helmholtz frequency increases.Both resonance peaks of the admittance functions in the two compartments decrease with increasing the amplitude of fluctuating external pressure coefficients or reference wind speed.

Deduction of Design Equations for Durability Performance Improvement of Voice Coil Type Linear Actuator for Servo Valve Operation

The precise hydraulic valve is widely used in various industrial fields like aircraft, automobile and general machinery. Linear actuator is the most important device for driving the precise hydraulic valve. The reliable operation of linear actuator has effects on the overall hydraulic system. The performance of linear actuator relies on frequency response and step response according to arbitrary input signal. In this paper, the analysis for the components of linear actuator is performed to satisfy the reliable operation and response characteristics through the reliability analysis, and also deducted the design equations to realize the reliable operation and fast response characteristics of voice coil type linear actuator for servo valve operation through the empirical knowledge of experts and electromagnetic theories. The design equations are suggested to determine the values of design parameters of linear actuator as like bobbin size, length of yoke and plunger and turn number of coil, and calculated the life test time of linear actuator for verification of reliability of the prototype. In addition, for reducing the life test time, the acceleration model of linear actuator is proposed and the acceleration factor is calculated considering the field operating conditions. And then, the achieved design values are verified through accelerated life test and performance tests using some prototypes of linear actuators adapted in servo valve.

Design equations for maximum stress concentration factors for concrete-filled steel tubular K-joints

Stress concentration factors(SCFs) for welded tubular joints can be decreased by filling the chord with concrete leading to a longer fatigue life. However, there are currently no design formula available in guidelines to predict the SCF of concrete-filled circular hollow section(CFCHS) K-joints, thus limiting their applicability in bridge design. To address this gap,finite element models for CFCHS K-joints were developed and compared against test results to ensure their accuracy. Then, a comprehensive parametric study was conducted to establish relationships between maximum SCFs and four variables: brace-to-chord diameter ratio(β), chord diameter-to-thickness ratio(2γ), brace-to-chord thickness ratio(τ), and the angle between braces and chord(θ). A total of 480 FE models were examined under three loading conditions including brace and chord loading: balanced axial force, chord axial force, and chord bending. Design equations to predict the maximum SCF for CFCHS Kjoints were established by multiple regression analyses of the numerical results. A comparison of maximum SCFs between circular hollow section(CHS) and CFCHS K-joints was made, and it was concluded that average reductions of 42% and 33% in maximum SCFs in CFCHS K-joints at the locations of the chord and brace were found compared to CHS joints for balanced axial force, respectively. Finally, a case study illustrating how to use the proposed equations for fatigue safety verification was presented.

AERODYNAMIC OPTIMIZATION FOR TURBINE BLADE BASED ON HIERARCHICAL FAIR COMPETITION GENETIC ALGORITHMS WITH DYNAMIC NICHE

A global optimization approach to turbine blade design based on hierarchical fair competition genetic algorithms with dynamic niche （HFCDN-GAs） coupled with Reynolds-averaged Navier-Stokes （RANS） equation is presented. In order to meet the search theory of GAs and the aerodynamic performances of turbine, Bezier curve is adopted to parameterize the turbine blade profile, and a fitness function pertaining to optimization is designed. The design variables are the control points＇ ordinates of characteristic polygon of Bezier curve representing the turbine blade profile. The object function is the maximum lift-drag ratio of the turbine blade. The constraint conditions take into account the leading and trailing edge metal angle, and the strength and aerodynamic performances of turbine blade. And the treatment method of the constraint conditions is the flexible penalty function. The convergence history of test function indicates that HFCDN-GAs can locate the global optimum within a few search steps and have high robustness. The lift-drag ratio of the optimized blade is 8.3% higher than that of the original one. The results show that the proposed global optimization approach is effective for turbine blade.

A new design approach for the established flow region of vertical,dilute-phase pneumatic conveyors

An analysis has been completed for a comprehensive set of vertical,dilute-phase pneumatic conveying pressure drop data from an investigation by Flatow.The data were collected in the established flow region for eight different materials conveyed in 0.05-,0.10-,0.20-m internal diameter,20-m tall steel risers.Particle velocities derived from the pressure drop data were used to develop an equation of motion that includes terms for pipe diameter,terminal velocity,coefficient of restitution,and particle shape.The best data fit was achieved using the actual gas density and the actual gas velocity adjusted for voidage.Adjusting the terminal velocity for voidage,an approach recommended by many investigators,did not improve the fit for reasons identified by the present research.Using the equation of motion,particle velocities were predicted and used to calculate total pressure drops that are within±15%of the measured values.The calculated values also produce the characteristic trough-shaped total pressure drop curves allowing the minimum pressure drop gas velocity to be determined without recourse to a separate correlation.A comparison with other studies using shorter risers indicates that data from these studies likely include acceleration effects.A separate study will investigate this observation further.

Shear behavior of ultra-high-performance concrete beams prestressed with external carbon fiber-reinforced polymer tendons

The ultra-high-performance concrete(UHPC)and fiber-reinforced polymer(FRP)are well-accepted high-performance materials in the field of civil engineering.The combination of these advanced materials could contribute to improvement of structural performance and corrosion resistance.Unfortunately,only limited studies are available for shear behavior of UHPC beams reinforced with FRP bars,and few suggestions exist for prediction methods for shear capacity.This paper presents an experimental investigation on the shear behavior of UHPC beams reinforced with glass FRP(GFRP)and prestressed with external carbon FRP(CFRP)tendons.The failure mode of all specimens with various shear span to depth ratios from 1.7 to 4.5 was diagonal tension failure.The shear span to depth ratio had a significant influence on the shear capacity,and the effective prestressing stress affected the crack propagation.The experimental results were then applied to evaluate the equations given in different codes/recommendations for FRPreinforced concrete structures or UHPC structures.The comparison results indicate that NF P 18-710 and JSCE CES82 could appropriately estimate shear capacity of the slender specimens with a shear span to depth ratio of 4.5.Further,a new shear design equation was proposed to take into account the effect of the shear span to depth ratio and the steel fiber content on shear capacity.

Degree of bending of concrete-filled rectangular hollow section K-joints under balanced-axial loadings

It has been found that the fatigue life of tubular joints is not only determined by the hot spot stress,but also by the stress distribution through the tube thickness represented as the degree of bending(DoB).Consequently,the DoB value should be determined to improve the accuracy of fatigue assessment for both stress-life curve and fracture mechanics methods.Currently,no DoB parametric formula is available for concrete-filled rectangular hollow section(CFRHS)K-joints,despite their wide use in bridge engineering.Therefore,a robust finite element(FE)analysis was carried out to calculate the DoB of CFRHS K-joints under balanced-axial loading.The FE model was developed and verified against a test result to ensure accuracy.A comprehensive parametric study including 190 models,was conducted to establish the relationships between the DoBs and four specific variables.Based on the numerical results,design equations to predict DoBs for CFRHS K-joints were proposed through multiple regression analysis.A reduction of 37.17%was discovered in the DoB,resulting in a decrease of 66.85%in the fatigue life.Inclusively,the CFRHS K-joints with same hot spot stresses,may have completely different fatigue lives due to the different DoBs.