Target reliability index for serviceability limit state of single piles

The objective is to develop an approach for the determination of the target reliability index for serviceability limit state(SLS) of single piles. This contributes to conducting the SLS reliability-based design(RBD) of piles. Based on a two-parameter,hyperbolic curve-fitting equation describing the load-settlement relation of piles, the SLS model factor is defined. Then, taking into account the uncertainties of load-settlement model, load and bearing capacity of piles, the formula for computing the SLS reliability index(βsls) is obtained using the mean value first order second moment(MVFOSM) method. Meanwhile, the limit state function for conducting the SLS reliability analysis by the Monte Carlo simulation(MCS) method is established. These two methods are finally applied to determine the SLS target reliability index. Herein, the limiting tolerable settlement(slt) is treated as a random variable. For illustration, four load test databases from South Africa are compiled again to conduct reliability analysis and present the recommended target reliability indices. The results indicate that the MVFOSM method overestimates βsls compared to that computed by the MCS method. Besides, both factor of safety(FS) and slt are key factors influencing βsls, so the combination of FS and βsls is welcome to be used for the SLS reliability analysis of piles when slt is determined. For smaller slt, pile types and soils conditions have significant influence on the SLS target reliability indices; for larger slt, slt is the major factor having influence on the SLS target reliability indices. This proves that slt is the most key parameter for the determination of the SLS target reliability index.

A continuum damage model for piezoelectric materials

In this paper, a constitutive model is proposed for piezoelectric material solids containing distributed cracks. The model is formulated in a framework of continuum damage mechanics using second rank tensors as internal variables. The Helrnhotlz free energy of piezoelectric mate- rials with damage is then expressed as a polynomial including the transformed strains, the electric field vector and the tensorial damage variables by using the integrity bases restricted by the initial orthotropic symmetry of the material. By using the Talreja＇s tensor valued internal state damage variables as well as the Helrnhotlz free energy of the piezoelectric material, the constitutive relations of piezoelectric materials with damage are derived. The model is applied to a special case of piezoelectric plate with transverse matrix cracks. With the Kirchhoff hypothesis of plate, the free vibration equations of the piezoelectric rectangular plate considering damage is established. By using Galerkin method, the equations are solved. Numerical results show the effect of the damage on the free vibration of the piezoelectric plate under the close-circuit condition, and the present results are compared with those of the three-dimensional theory.

Effect of electroacupuncture on muscle state and infrared thermogram changes in patients with acute lumbar muscle sprain

OBJECTIVE:To observe the effect of electroacupuncture(EA) on force-displacement value(FDV)of muscle state and the temperature index of infrared thermogram in patients with acute lumbar muscle sprain.METHODS:Patients with acute lumbar muscle sprain were randomly divided into a medication group and an EA group.The medication group(n-60) were treated with diclofenac sodium dual release enteric-coated capsules,75 mg per day for 7days.The EA group(n = 60) received EA at bilateral Houxi(SI 3),Jiaji(EX-B2),and Ashi points,at 20-30 mm depth and 10-25 Hz frequency for 20 min daily for 7 days.Muscle states were determined by measuring FDVs of the bilateral lumbar muscle with a Myotonometer fast muscle state detector.The temperature index of the lumbar skin was measured before and after treatment with a Fluke Ti30 non-refrigerated focal plane infrared thermal imaging detector.RESULTS:There were no significant pre-treatment differences between the medication group and the EA group in mean FDV(P = 0.052) or temperature index of the lumbar skin(P = 0.25).The cure rate was 63.3%in the EA group and 53.3%in the medication group.The total efficacy in the EA group(93.3%) was not significantly different from that in the medication group(86.6%,P = 0.204).After treatment,the mean FDV of the lumbar muscle significantly increased in both groups(P < 0.05 for both groups);the FDV increase in the EA group was significantly higher than in the medication group(P = 0.015).The temperature index was also significantly increased in both groups(P < 0.05 for both groups);the infrared thermogram in the EA group indicated significantly greater recovery compared to the medication group(P = 0.026).CONCLUSION:Both EA and diclofenac sodium markedly improved acute lumbar sprain,but EA better improved the rehabilitation and regeneration of FDVs and temperature index of infrared thermogram of the muscle.