Masonry infill walls in reinforced concrete frames as a source of structural damping

This paper presents the results of an experimental study on the determination of damping characteristics of bare, masonry infilled, and carbon fiber reinforced polymer retrofitted infilled reinforced concrete (RC) frames. It is well known that the masonry infills are used as partitioning walls having significant effect on the damping characteristics of structures as well as contribution to the lateral stiffness and strength. The main portion of the input energy imparted to the structure during earthquakes is dissipated through hysteretic and damping energies. The equivalent damping definition is used to reflect various damping mechanisms globally. In this study, the equivalent damping ratio of carbon fiber reinforced polymer retrofitted infilled RC systems is quantified through a series of 1/3‐scaled, one‐bay, one‐story frames. Quasi‐static tests are carried out on eight specimens with two different loading patterns: one‐cycled and three‐cycled displacement histories and the pseudo‐dynamic tests performed on eight specimens for selected acceleration record scaled at three different PGA levels with two inertia mass conditions. The results of the experimental studies are evaluated in two phases: (i) equivalent damping is determined for experimentally obtained cycles from quasi‐static and pseudo‐dynamic tests; and (ii) an iterative procedure is developed on the basis of the energy balance formulation to determine the equivalent damping ratio. On the basis of the results of these evaluations, equivalent damping of levels of 5%, 12%, and 14% can be used for bare, infilled, and retrofitted infilled RC frames, respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

Vertical acceleration demands on column lines of steel moment‐resisting frames

In this paper, vertical peak floor acceleration (PFA_v) demands on elastic multistory buildings are statistically evaluated using recorded ground motions. These demands are applicable to the assessment of nonstructural components that are rigid in the vertical direction and located at column lines or next to columns. Hence, PFA_v demands of the floor system away from column lines and their effects on nonstructural components are not addressed. This study is motivated by the questionable general assumption that typical buildings are considered to be relatively flexible in the horizontal (lateral) direction but relatively rigid in the vertical (longitudinal) direction. Consequently, only few papers address the evaluation of vertical component acceleration demands throughout a building, and there is no consensus on the relevance of vertical accelerations in buildings. The results presented in this study show that the vertical ground acceleration demands are amplified throughout the column line of a steel frame structure. This amplification is in many cases significant, depending on the vertical stiffness of the load‐bearing system, damping ratio, and the location of the nonstructural component in the building. From these outcomes it can be concluded that the perception of a rigid‐body response of the column lines in the vertical direction is highly questionable, and further research on this topic is required. Copyright © 2016 John Wiley & Sons, Ltd.     

Simplified macro‐model for infill masonry walls considering the out‐of‐plane behaviour

One of the main challenges in earthquake risk mitigation is the assessment of existing buildings not designed according to modern codes and the development of effective techniques to strengthen these structures. Particular attention should be given to RC frame structures with masonry infill panels, as demonstrated by their poor performance in recent earthquakes in Europe. Understanding the seismic behaviour of masonry‐infilled RC frames presents one of the most difficult problems in structural engineering. Analytical tools to evaluate infill–frame interaction and the failure mechanisms need to be further studied. This research intends to develop a simplified macro‐model that takes into account the out‐of‐plane behaviour of the infill panels and the corresponding in‐plane and out‐of‐plane interaction when subjected to seismic loadings. Finally, a vulnerability assessment of an RC building will be performed in order to evaluate the influence of the out‐of‐plane consideration in the building response. Copyright © 2015 John Wiley & Sons, Ltd.     

响应面法优化罗非鱼(Oreochromis niloticus)鱼排蛋白分段酶解工艺

采用生物蛋白酶酶解罗非鱼鱼排蛋白,以水解度(DH)为指标,进行了单酶、复合酶酶解效果的比较分析,并利用响应面分析方法(RSM)对酶解参数进行优化。结果表明,采用风味蛋白酶和木瓜蛋白酶双酶组合分段酶解,固定总酶添加量为3.0%、双酶复合比2:1、酶解时间3h、分段酶解时间比0.6:1,酶解温度56℃,分段酶解pH为7.0和6.2时,酶解效果最佳,罗非鱼鱼排蛋白水解度达到32.49%,酶解产物中游离氨基酸含量达32.84mg/g鱼排,占罗非鱼鱼排总氨基酸含量的25.43%,其中呈味氨基酸含量达18.48%,必需氨基酸含量达67.96%。     

变截面门式刚架稳定及地震反应研究进展

变截面轻钢门式刚架为我国单层大跨度工业和仓储建筑的主要结构形式.本文简要回顾了国内外变截面轻钢门式刚架稳定和地震反应研究的概况,介绍了其稳定分析及稳定设计方法的新进展以及地震反应理论分析、实验研究和分析方法的新进展,指出了目前在稳定和动反应研究及工程应用中存在的问题.针对我国相关现行规范在变截面门式刚架稳定和抗震设计方面规定的不足和存在的缺陷,提出了在稳定、地震反应及极限承载能力的判定方法等方面的研究建议.     

Seismic design of space steel frames using advanced methods of analysis

A rational and efficient seismic design methodology for regular space steel frames using an advanced time domain finite element method of analysis that takes into account geometrical and material nonlinearities is presented. Seismic loads are applied in the form of Eurocode 8 spectrum compatible real accelerograms along the two horizontal directions of the frame. The iterative design procedure starts with assumed member sections, continues with the response checks for the damage, ultimate and service limit states and ends with the adjustment of member sizes so as all the response checks to be satisfied for all limit states. Thus, the proposed design method deals with nonlinearities and member interactions at the global level and consequently separate member capacity checks through the interaction equations of Eurocode 3 or the usage of the conservative and crude q-factor of Eurocode 8 are not required. Two numerical examples dealing with the design of (a) a space three storey steel frame with one bay in both horizontal directions and (b) a space seven storey steel frame with two and three bays along its two horizontal directions are presented to illustrate the method and demonstrate its advantages.     

Shake table tests of small- and full-scale laminated timber frames with moment connections

This paper describes the results of shake-table tests of laminated timber frames with moment beam-to-column connections. The objective of the study was to investigate the dynamic behaviour of small-scale (1:4) and full-scale (1:1) frames in regard to residual system deformations and changes in dynamic characteristic due to the progressing damage in the dowel-type connections. Different frame designs with and without connection reinforcement were tested. The experiments demonstrated that the frames were capable of resisting strong ground motions and undergoing large drifts without failure. Moment-resisting frames with correctly designed connections can behave as a self-centering system with columns and beams deforming elastically and connections functioning as energy dissipative links.     

Seismic Performance of RC Frames Designed to Eurocode 8 or to the Greek Codes 2000

For the first time after the finalisation of the European Norm for seismic design of buildings (Eurocode 8 – EC8),the performance of RC buildings designed with this code is evaluated through systematic nonlinear analyses. Regular 4-, 8- or 12-storey RC frames are designed for a PGA of 0.2 or 0.4 g and to one of the three alternative ductility classes in EC8. As the Eurocodes are meant to replace soon existing national codes, design and performance is also compared to that of similar frames designed with the 2000 Greek national codes. The performance of alternative designs under the life-safety (475 years) and the damage limitation (95 years) earthquakes is evaluated through nonlinear seismic response analyses. The large difference in material quantities and detailing of the alternative designs does not translate into large differences in performance. Design for either Ductility Class High (H) or Medium (M) of EC8 is much more cost-effective than design for Ductility Class Low (L), even in moderate seismicity. It is also much more cost-effective than design to the 2000 Greek national codes.     

Is there utility in rigorous combinations of VLBI and GPS Earth orientation parameters?

Combinations of station coordinates and velocities from independent space-geodetic techniques have long been the standard method to realize robust global terrestrial reference frames (TRFs). In principle, the particular strengths of one observing method can compensate for weaknesses in others if the combination is properly constructed, suitable weights are found, and accurate co-location ties are available. More recently, the methodology has been extended to combine time-series of results at the normal equation level. This allows Earth orientation parameters (EOPs) to be included and aligned in a fully consistent way with the TRF. While the utility of such multi-technique combinations is generally recognized for the reference frame, the benefits for the EOPs are yet to be quantitatively assessed. In this contribution, which is a sequel to a recent paper on co-location ties (Ray and Altamimi in J Geod 79(4–5): 189–195, 2005), we have studied test combinations of very long baseline interferometry (VLBI) and Global Positioning System (GPS) time-series solutions to evaluate the effects on combined EOP measurements compared with geophysical excitations. One expects any effect to be small, considering that GPS dominates the polar motion estimates due to its relatively dense and uniform global network coverage, high precision, continuous daily sampling, and homogeneity, while VLBI alone observes UT1-UTC. Presently, although clearly desirable, we see no practical method to rigorously include the GPS estimates of length-of-day variations due to significant time-varying biases. Nevertheless, our results, which are the first of this type, indicate that more accurate polar motion from GPS contributes to improved UT1-UTC results from VLBI. The situation with combined polar motion is more complex. The VLBI data contribute directly only very slightly, if at all, with an impact that is probably affected by the weakness of the current VLBI networks (small size and sparseness) and the quality of local ties relating the VLBI and GPS frames. Instead, the VLBI polar motion information is used primarily in rotationally aligning the VLBI and GPS frames, thereby reducing the dependence on co-location tie information. Further research is needed to determine an optimal VLBI-GPS combination strategy that yields the highest quality EOP estimates. Improved local ties (including internal systematic effects within the techniques) will be critically important in such an effort.