Seismic force modification factor for ductile structures

The earthquake forces used in design codes of buildings should be theoretically determinable. This work examines the seismic force modification factor R based on elastic-plastic time-history earthquake analysis of SDOF systems, wherein the hys-teresis models are elastic-perfectly-plastic (EPP), elastic-linearly-hardening (ELH), shear-slipped and bilinear-elastic. The latter two models are analysed for separating the effect of the ductility and the energy-dissipating capacity. Three-hundred eighty-eight earthquake records from different site conditions are used in analysis. The ductility is taken to be 2, 3, 4, 5 and 6, with the damping ratio being 0.02, 0.035 and 0.05 respectively. The post-yield stiffness ratios 0.0, 0.1 and 0.2 are used in the analysis. The R spectra are standardized by the characteristic period of the earthquake records, which leads to a much smaller scatter in averaged numerical results. It was found that the most important factor determining R is the ductility. R increases more than linearly with ductility. The energy-dissipating capacity, damping and the post-yield stiffness are the less important factors. The energy dissipating capacity is important only for structures with short period and moderate period (0.3≤T/Tg<5.0). For EPP and ELH models, R for 0.05 damping is 10% to 15% smaller than for 0.02 damping. For EPP and ELH models, greater post-yield stiffness leads to greater R, but the influence of post-yield stiffness is obvious only when the post-yield stiffness is less than 10% of the initial stiffness. By means of statistical regression analysis the relation of the seismic force modification factor R with the natural period of the system and ductility for EPP and ELH models were established for each site and soil condition.

PROPER CONDITIONS OF MESHING FOR Hy-Vo SILENT CHAIN AND SPROCKET

Proper meshing of Hy-Vo silent chain and sprocket is important for realizing the transmission of the silent chain with more efficiency and less noise. Based on the study of the meshing theory of the Hy-Vo silent chain with the sprocket and the roll cutting machining principle of the sprocket with the hob, the proper conditions of the meshing for the Hy-Vo silent chain and the sprocket are put forward with the variable pitch characteristic of the Hy-Vo silent chain taken into consideration, and the proper meshing design method on the condition that the value of the link tooth pressure angle is unequal to the value of the sprocket tooth pressure angle is studied. Experiments show that this new design method is feasible. In addition, the design of the pitch, the sprocket tooth pressure angle and the fillet radius of the sprocket addendum circle are studied. It is crucial for guiding the design of the hob which cuts the Hy-Vo silent chain sprocket.

Analysis of lubrication performance for internal meshing gear pair considering vibration

The thermal elasto-hydrodynamic lubrication characteristics of the internal meshing gears in a planetary gear train under vibrations were examined considering the influence of the modification coefficient and time-varying meshing stiffness.Based on dynamic theory of the gear system,a dynamic model of the planetary gear train was established.The lubrication performances of modified gear systems under vibrations and static loads were analyzed.Compared with other transmission types,the best lubrication effect could be produced by the positive transmission.A thicker lubricating oil film could be formed,and the friction coefficient and oil film flash temperature are the smallest.Increasing modification coefficient improves the lubrication performance continuously but intensifies the engage-in and tooth-change impact.For the planetary and inner gears,the increase in the modification coefficient also leads a decrease in the oil film stiffness.

MESHING THEORY AND DESIGN METHOD OF NEW SILENT CHAIN AND SPROCKET

Based on the study of the meshing theory of a new silent chain and sprockets, and the rolling cutting theory of sprocket and hob, the harmonious relations of dominating dimensions among the new silent chain, sprocket and hob is build, the meshing conditions are expatiated, and the resolved expression, which can instruct design and calculation, is educed. The tests show that the meshing design method is feasible.

Thermal elastohydrodynamic lubrication of modified gear system considering vibration

The thermal elastohydrodynamic lubrication characteristics of a modified gear system under a dynamic load were investigated,including the influence of the modification coefficient and vibrations.Based on the dynamic theory of gear systems,a six-degree-of-freedom tribo-dynamics model was established.Thermal elastohydrodynamic lubrication characteristics of a modified gear system under vibrations and a static load were analyzed.The results showed that the positive transmission gear system exhibited the better lubrication effect compared with other transmission types.A thick lubricating oil film could be formed,and the friction coefficient between the teeth and the oil film flash temperature were the smallest.As the modification coefficient increased,the lubrication condition was continuously improved,and the scuffing load capacity was enhanced.The increment of the modification coefficient increased the meshing stiffness of the gear system but reduced the stiffness of the oil film.

Study of a New Drafting System of Rubbed Roving Frame

This paper puts forward a new drafting system of the rubbed roving frame, which consists of a nine-link gear, two slipping gears. It has brought forward a new design method of the nine-link gear and the slipping gears, and set up approximate formulas for modification coefficients of gears for the first time. And the principles of transmitting rate designing for the system are given. The calculating results demonstrate that the new design method satisfies the demands of processing technology. This mechanism has been used successfully in the kind of rubbed roving frame.

Effect of Variable Concrete Strength on the Behavior of Buckling Restrained Braced Frames under Blast Load

BRBF(buckling restrained braced frame)is a relatively new lateral force resisting system for building structures.BRBFs are used mostly to resist seismic force due to their high ductility after yielding and the ability to absorb higher strain energy.ASCE(American Society of Civil Engineers)first permits the use of BRBFs as a single seismic force-resisting system by quantifying the seismic parameters such as response modification coefficient(R),over-strength factor(Ωo)and deflection amplification factor(Cd)for a structure built with BRBF,in their 2010 code(ASCE 7-10).But it has not been investigated how a structure built with BRBF,which is primarily designed to resist seismic force,and behaves under sudden occurrence of a blast load.This research investigates the performance of a BRBF subjected to blast loading.In other words,this paper focuses on the effect of blast loading on BRBF.The architype for this investigation is a chevron type braced frame.The frame is subjected to a short duration blast load that lasts only 21.7 mili-second(ms).Blast loading effects on the braced frame are assessed by identifying the weakest plane of failure,deformation characteristics and out of plane bending.The research investigates how the properties of the surrounding concrete,especially compressive strength,affect the overall strength of the BRBF on resisting blast loading.It is observed that the compressive strength of the surrounding concrete plays a significant role in reducing the deformation characteristics,both in-plane and out-of-plane.

Method for generating non-circular gear with addendum modification and its application in transplanting mechanism

With a focus on the design of tooth profiles of non-circular gears with addendum modifications that conform to the given complex transmission ratio curves and based on a series of discrete point sets on the pitch curves,the criteria for tooth profile distortion and undercut in non-circular gears were proposed.With the constraint of no tooth profile distortion and undercut,the addendum modification coefficient was introduced into the calculation of the distorted and undercut segments of the tooth profile of a non-circular gear,and the addendum modification coefficient of each contact point of the non-circular gear was obtained.Based on the generating principle for gear shaping with gear cutters,a theoretical model for calculating the tooth profile of non-circular gears with addendum modification was derived.The cutting and radial feeding motions of the pinion cutter were ignored,and only the meshing motion was considered.The involute tooth profiles of the pinion cutter enveloped the tooth profile of the non-circular gear.3D automatic non-circular gear model generation software was developed,which was a secondary development product of the software UG.A non-circular gear in a rice potted seedling transplanting mechanism was designed,and the transplanter was developed and tested.The test results showed that the designed tooth profile of non-circular gear achieved the variable transmission ratios required by the transplanting mechanism.When the transplanting efficiencies were 140 plants/min,160 plants/min and 180 plants/min,the transplanter completed the rice potted seedling transplanting operation with high quality.