This paper compares the seismic load of a 5MW wind turbine supported by a 100-m-high prestressed concrete tower calculated via time history analysis and response spectrum analysis using elastic acceleration spectrum provided by the China Aseismic Code for Buildings. With 5% damping ratio, the fixed-based Multi-degree of freedom model and Finite element model considering soil structure interaction are used for response spectrum analysis and time history analysis, respectively. The results indicated that the seismic load calculated by response spectrum analysis is significantly larger than the results associated with the time history analysis method. It implies that the seismic load determined from common building code procedures along with other loads for wind turbine foundation design is too conservative. Within this paper, the effects of damping ratio, horizontal acceleration amplitude, spring stiffness and damping coefficient of foundation on the seismic load of the prestressed concrete wind turbine tower are discussed. It is shown that the seismic load with mode damping ratio for the prestressed concrete wind turbine tower is not significant when compared with traditional tubular steel designs. The maximum moment demand at the base of the tower may be controlled by earthquake loading as the seismic fortification intensity lever is more than seven. The foundation spring stiffness has a immensely impact on the base bending moment and the natural frequency. Finally, seismic load should be considered in more detail when designing wind turbines that are supported by concrete towers, particularly for turbine’s over 100-m tall and located in seismically active zones.

This study is devoted to investigate the effects of mass eccentricity in seismic responses of base-isolated structures subjected to near field ground motions. Superstructures with 3, 6 and 9 stories and aspect ratios equal to 1, 2 and 3 have been idealized as steel special moment frames resting on a reasonable variety of Triple Concave Friction Pendulum (TCFP) bearings considering different period and damping ratios for the isolators. Three-dimensional linear superstructure mounted on nonlinear isolators are subjected to 3 components of near-field ground motions. Under 25 near-field ground motions, effects of mass eccentricity on the main system parameters are studied. These parameters are selected as the main engineering demands including maximum isolator displacement and base shear as well as peak superstructure acceleration. The results indicate that the mass eccentricities has not a remarkable effect on isolator displacement. In contrary to displacement, torsional effect of mass eccentricity raise the base shear up to 1.75 times in a three-story superstructure. Additionally, mass eccentricity can amplify the roof acceleration of a nine-story model approximately 3 times in comparison with a symmetric superstructure. It is also concluded that eccentricity in the direction of the subjected earthquake has the most impact on base shear while the isolator displacement and roof acceleration has mostly influenced by the eccentricity perpendicular to the earthquake path.

The seismic performance levels are discrete damage states selected from among the infinite spectrum of possible damage states that buildings could experience as a result of earthquake response. The observation of building damage during strong motion earthquakes showed that correlation of structural damage with a single parameter such as peak ground acceleration or the total seismic duration is low while peak ground acceleration is often used as a main seismic parameter to evaluate seismic performance of structures. Main objective of this study is to determine the relationship between several seismic acceleration parameters and the Target Displacement (TD) of steel frame structures, which is an important parameter to identify performance levels. For this purpose, first, nonlinear analysis is performed on the SAC 3- and 9-story frames subjected to several far-field earthquakes and then target displacements and seismic parameters are calculated for each structure.The relationship between the target displacement and seismic parameters is evaluated in the form of correlation coefficient. It is shown that PGA has poor correlation with the target displacement. On the other hand, HOUSNER intensity, spectral pseudo-acceleration, spectral pseudo-velocity and peak ground velocity exhibit strong correlation with TD.

Microtremor measurement is a precise and applicable technique for evaluating structural dynamic characteristics and vulnerability index of historical buildings. In this research a historical citadel in Iran has been considered. Karim Khan Citadel (Arg-e Karim Khan) is a huge masonry structure which has been built in the 17th century in Shiraz, Iran. The plan of this building has a rectangular shape and has a circular tower in each corner. The height of each three story circular tower is 14 m and the height of walls between each two towers is 12 m. One of these towers has been swerved and for preventing its collapse, concrete was injected to the foundation of this tower. To study seismic behavior and vulnerability of the swerved tower and compare it with other straight tower, microtremor measurements were performed. Measurements were done on the center of each tower and its basement simultaneously. For determining natural frequency and damping ratio of each tower, Floor Spectral Ratio (FSR) and Random Decrement Method (RDM) were used, respectively. Results show that the natural frequency and damping ratio of the swerved tower are 1.9 Hz and 1.55 % while dynamic parameters of the straight tower are 2.12 Hz and 3.86 %, respectively. Also the towers frequencies are very different to the site frequency (4.18 Hz), therefore the resonance phenomenon isn’t probable. In addition, the vulnerability indexes of the swerved and straight towers were calculated 131.31 and 76.9, respectively, which shows that the swerved tower is more vulnerable.

Sliding foundations is a technique to suppress seismic loads applied to structures. There are many studies showing that sliding foundations are efficient specially for low rise buildings, however most of them have ignored the effects of vertical components of the earthquake records on the behavior of such bases. This paper focuses on influences of sliding foundations on seismic behavior of low rise buildings, for real cases. For this purpose, vertical component of earthquakes are considered as well as inherent properties of foundation material such as coefficient of Restitution (COR). Furthermore, variation of friction coefficient during the earthquake is considered. COR is utilized to consider bouncing of the structure after separation of the foundation, occurred for extreme downward vertical accelerations (greater than gravitational acceleration). Variation of friction coefficient is considered based on a new study, showing that the coefficient of friction depends on instantaneous amplitude and frequency of the vertical excitation. The obtained results show that vertical component of earthquake affects the behavior of the sliding base substantially. It is also demonstrated that providing material for the sliding base with higher COR is advantageous in decreasing structural acceleration response. Furthermore, the coefficient of friction is really lower than the regularly assumed values and therefore, leads to smaller structural acceleration response but mostly greater residual displacements.

THIS IS THE REVISED VERSION OF THE PAPER A-10-581-3, CONSIDERED AS "MAJOR REVISION": One of the best methods to improve structural seismic behavior is to strengthen the infills by shotcreting. Most rehabilitation codes have a special part for masonry buildings and masonry infill panels. However they are completely silent for infills improved by concrete covers, probably for the lack of sufficient experimental test data. This paper focuses on the ultimate strength and modification factor of this type of infill panels, based on some experimental studies. The proposed formula of the existing codes for the equivalent width of the masonry infill panels is improved for the ultimate strength of shotcreted infill panels. It is also shown that the modification factors of the masonry and clay tile infill panels are downgraded and upgraded, respectively, if they are rehabilitated by concrete covers. The envelopes of the load-displacement behavior of the specimens are applied to calculate the modification factor, rather than the standard back bone curves. It is shown that they give more conservative values for the m-factor. Subsequently, some suggestions are proposed to estimate m-factor of shotcreted infill panels.

Bridges normally undergo nonlinear deformations during a near field strong ground motion resulting in a critical deviation of their columns from the plumb state due to considerable residual deformations. These excessive residual deformations make a bridge, which has not collapsed, ‘irreparable’ and in turn ‘not operable.’ Therefore, reasonable prediction of these types of bridge piers deformations is of great importance in order to evaluate the serviceability of bridges subjected to a seismic scenario. Conventional hysteresis models formulated for typical concrete columns are normally used for this purpose which most of times fail to correctly predict the residual deformations occurred as a result of a one-sided or directivity pulse excitation. The present research aims at development of a peak oriented hysteresis model being able to regenerate residual deformations more reasonable compared to the conventional hysteresis models. This multi linear peak oriented model considers strength deterioration in each half cycle in addition to stiffness degradations in unloading cycles. Yielding points differ in both positive and negative sides of the hysteresis model that enables us to define a different elastic stiffness of both sides in asymmetric concrete sections. Another remarkable property of this model is breaking points and strength deterioration in unloading and reloading stages. This work also compares the obtained results to the conventional hysteresis models, namely bilinear, Clough, Q-Hyst, Takeda and Bouc-Wen in terms of prediction of residual nonlinear deformations in cyclic or dynamic analysis of reinforced concrete single-column bridge piers. The obtained results prove higher relative accuracy of the proposed model.

In this paper, the probabilistic seismic performance of vertically irregular steel buildings, considering soil-structure interaction effects, is evaluated. Various irregular distributions of structural properties, including mass, stiffness and strength along the height of three-dimensional moment resisting steel frames were intended. The finite element model of soil medium was created with solid elements below the structure. The nonlinear material behavior of soil was considered as well. Nonlinear incremental dynamic analysis was performed to evaluate the flexible-base structural performance in the framework of probabilistic performance-based earthquake engineering. According to the median curves of intensity-demand of structures, it is concluded that non-uniform height-wise distribution of lateral resistance properties of steel structures varies the displacement demand and the seismic capacity of the irregular frames, compare to the regular structure. The capacity variation of most irregular frames is more obvious at the nonlinear phase of structural behavior. Due to the foundation flexibility, the damage concentration raises in the bottom floor and the irregularity increase the seismic demands of the lower floors of the system. Among all the irregular steel frames, the average increase of the displacement demand and reduction of the seismic capacity are maximal for the strength and concurrent variation of stiffness and strength irregularity models, respectively. Additionally, mass irregularity shows minor influence in the seismic demand and capacity variations of the steel frames. The predominant influence of stiffness and strength irregularities (soft and weak story) is observed in reduction of the structural ductility factor and the mean annual frequency of exceeding limit states.

This paper presents an evaluation on lateral cyclic behaviors of precast concrete columns using a steel box connection through experimental investigation. The test consisted of one monolithic reinforced concrete column as a reference and five precast concrete columns. All specimens had identical dimensions of 0.25 x 0.25 m2 cross sectional area and 1.7 m in height with a longitudinal reinforcement ratio of 0.0152. Materials used for all specimens were also from the same batch. The study was aimed at understanding the design concept of the steel connecting box and detailing of column reinforcement for avoiding the brittle failure of precast concrete frame buildings. The experimental results show that without premature failure in welding or nut slipping, depending largely on the reinforcement details, the precast system with a steel box connection can be effectively used. Flexural failure mode with a ductile mechanism can be achieved to resemble the monolithic one. With a higher relative stiffness and capacities of the designed connecting box, the precast columns show a higher capacity as the failure section was shifted to an upper level. Hence, it can be said that the proper details of precast concrete columns contain acceptable seismic performances e.g. ultimate capacity, stiffness, energy dissipation, and capacity degradation under repeated loading.

Among important issues in progressive collapse behavior of a building is tracking down the type and location of the damaged elements. This paper deals with identifying the distribution of collapse from the first element to the entire building due to earthquake loads. Here, 3D collapse propagations in symmetric and asymmetric reinforced concrete buildings are compared using nonlinear time history analyses. The variables of such analyses are earthquake load intensity and the level of in plan one directional mass eccentricity. Results show that collapse distribution is dependent on the degree of asymmetry in building. Some patterns to predict progressive collapse scenarios in similar symmetric and asymmetric buildings are also determined. One main pattern shows that the propagation of collapse is horizontal through the stories, but not vertical through the height of the buildings. Spread of the collapse is independent of the earthquake records also according to the results, damage concentration is larger in places with larger mass concentration.

This paper tried to analyze the behavior of a typical bridge and the effect of its skew degree on its behavior to near-field earthquakes. To this end, the seismic behavior of a number of typical bridges with same spans and different skew degrees was studied under near-field and far-field earthquakes. Non-linear static analyses (pushover analyses) were performed to determine the performance parameters of the bridge in each model. Non-linear time history dynamic analyses were also performed on the models to analyze the dynamic behavior and deformations of bridge components under near-field and far-field earthquakes. The responses of models, such as their displacement, base shear, and axial forces of columns to earthquakes under study are presented in the following sections. Results indicated that the base shear and displacement of the superstructure in near-field earthquakes without velocity pulse and far-field earthquakes are about or less than the corresponding values of the bridge performance point. Moreover, in the case of near-field earthquakes with velocity pulses the values of these parameters showed an increase. It was also revealed that an increase in the skew degree of the bridge led to an increase in the axial forces in columns and transverse displacement of the bridge.

This paper presents numerical and theoretical studies on the stability of shallow shield tunnel face found in cohesive-frictional soil. The minimum limit support pressure was determined by superposition method; it was calculated by multiplying soil cohesion, surcharge load, and soil weight by their corresponding coefficients. The varying characteristics of these coefficients with soil friction angle and tunnel cover-to-diameter ratio were obtained by wedge model and numerical simulation. The face stability of shallow shield tunnel with seepage was studied by deformation and seepage coupled numerical simulation; the constitutive model used in the analysis was elastic-perfectly plastic Mohr–Coulomb model. The failure mode of tunnel face was shown related to water level. By considering the effect of seepage on failure mode, the wedge model was modified to calculate the limit support pressure under seepage condition. The water head around the tunnel face was fitted by an exponential function, and then an analytical solution to the limit support pressure under seepage condition was deduced. The variations in the limit support pressure on strength parameters of soil and water lever compare well with the numerical results. The modified wedge model was employed to analyze the tunnel face stability of Qianjiang cross-river shield tunnel. The influence of tide on the limit support pressure was obtained, and the calculated limit support pressure by the modified wedge model is consistent with the numerical result.

In this study, the shear strength parameters of the Kaolinite clay, as the control material, and the Kaolinite clay reinforced by different percentages of two different types of crumb rubber content have been evaluated. The consolidated drained and unconsolidated undrained triaxial and California bearing ratio tests have been conducted on the control and crumb rubber reinforced soils. Addition of crumb rubber would improve shear strength parameters such as cohesion, friction and dilation angles, stiffness and the ductility of the reinforced soil. 5, 10 and 15 % (by the weight of dry soil) of crumb rubber content were used in this study which were undergone confining stress levels of 100, 200 and 300 kPa and an optimum crumb rubber content is found, which results in the maximum bearing capacity of the soil. Also, due to the non-linearity of the failure mode of reinforced soil and inadequacy of Mohr–Columb envelope for describing the behaviour, a failure mode is proposed for the clay soils reinforced by crumb rubber. This failure criterion is useful for failure envelope of clay-rubber matrix.

Pile load tests and numerical analysis of a small-scale model pile in unsaturated clayey soil are presented in this paper. A small-scale model pile was simulated to bear a static axial loading in unsaturated soil using finite element method. All parameters used in the finite element method were obtained in laboratory tests, including the direct shear test, interface direct shear test, and filter paper method. The numerical analysis results were compared with the pile load test results. The results show that the general trend of pile load and pile head settlement relationship obtained by the numerical analysis shows a good consistence with the pile load test results. With increasing water content of the soil, the matric suction, dilatancy angle and shear strength decrease, and consequently the ultimate bearing capacity of pile decreases.

It is vital to control the settlement of ultra-high voltage and long span tower foundation because of the difficult construction and strict deformation control. Based on the thinking of deformation compatibility, the mechanical model of deformation compatibility between pile and soil is established. Relying on the long span tower project Lingzhou–Shaoxing ±800 kV DC transmission lines across the Yangtze River, through checking ultimate bearing capacity of existing pile foundation, it can be obtained that the present design foundation can effectively meet the upper 200–220 t load, but it cannot meet the load requirements about 300 t in the construction. The failures of tower foundation mainly display that piles cut into the soil with penetration type in the early condition. With the load increasing, the shallow soil and infrastructure gradually damage with the whole cap sinking, cushion layer destruction and the surrounding soil uplifting. As a result, tower foundation is unable to withstand the effect of upper overload and the whole tower becomes shear failure. The treatment scheme was proposed that it can improve the cushion thickness and strength combined with grouting consolidation to soil around the piles. Thus, the stability of tower foundation improves significantly and settlement was controlled within the permitted range of below 10 mm, which can meet the structure requirements. The results of numerical simulation based on deformation compatibility between pile and soil coincide well with field measured results.

This paper proposes a modified strain wedge (MSW) model for nonlinear analysis of laterally loaded single piles in clays. The MSW model is used to calculate the soil resistance under increasing pile deflection. The stress–strain behavior of clays in the MSW, which is needed to calculate the soil resistance, is described in terms of both hyperbolic and bilinear stress–strain relationships. The subgrade reaction modulus of soil below the MSW is assumed to equal the conventional subgrade reaction modulus and to remain constant under the lateral loading of the pile. The applicability of the proposed model was verified by eight case histories. The results indicate that (1) the predicted results are consistent with the measurements for all eight full-scale tested piles; (2) the bilinear stress–strain relationship is not recommended for clays because the clays usually have a large ε50 and, thus, they exhibit a linear behavior in the MSW during loading; (3) the predicted pile response is less sensitive to the effective friction angle than to the undrained shear strength; and (4) the proposed MSW model applies to normally consolidated clays and to overconsolidated clays until they reach their peak strength.

In this study, an assessment to excess pore water pressure generated around a single pile and pile group excited by two opposite rotary machines embedded in saturated sandy soil was considered experimentally. A small-scale physical model was manufactured to accomplish the experimental work in the laboratory. The physical model consists of: two small motors supplied with eccentric mass of 0.012 kg and eccentric distance (20 mm) representing the two opposite rotary machines, an aluminum shaft 20 mm in diameter as the pile, and a steel plate with dimensions of (160 × 160 × 20 mm) as a pile cap. The experimental work was achieved taking the following parameters into considerations: pile embedment depth ratio (L/d), spacing between piles (S) and operating frequency of the rotary machines. Twelve tests were conducted in medium dense fine sandy soil with 60 % relative density. In all these tests, the change in excess pore water pressure was measured around the pile at two spots: at the middle of the pile and at its tip. The results revealed that the generation of excess pore water pressure was affected by the following parameters: slenderness ratio of the pile, operating frequency of the machines, and the soil permeability. However, for all cases, it was found that the pore water pressure generated during operation was not greater than 20 % of the initial hydrostatic pressure. Using pile foundation reduced the amplitude of vertical vibration by about (300 %) for all operating frequencies, lengths of piles, pile spacings and number of piles. In addition, the presence of piles reduced the disturbance (fluctuation) in this amplitude by about (400 %). For single pile, and under the same operating frequency, a small decrease in the amplitude of vertical vibration resulted from increasing the length of the pile.

To reveal the deformation mechanism during tunneling in deep soft ground, triaxial unloading confining pressure tests and triaxial unloading creep tests were carried out on sandy mudstone specimens to study the dilatancy and fracturing behavior of soft rock. In the triaxial unloading confining pressure tests, the stress path and different unloading rates were considered to reflect the unloading characteristics of the excavation methods. The unloading rate effects and the rock damage evolution law are studied. The following conclusions are obtained from the results. Firstly, when the unloading rate is smooth, the peak strengths and deviatoric stress–strain curves under the unloading condition are close to those under the conventional loading condition. Secondly, the post-peak brittle characteristics are more apparent with the increasing unloading rates. Thirdly, the soft rock undergoes five deformation and failure regimes of elasticity, pre-peak unloading damage–dilatancy, post-peak brittle drop, linear strain softening and residual perfect plasticity under quasi-static smooth unloading of mechanized excavation which is mainly focused on in this study. Fourthly, the damage evolution law at the pre-peak damage–dilatancy stage follows an exponential function. Fifthly, during the post-peak stages, multistage microfractures are initiated, propagated and finally coalesced forming a shear-fragmentation band with a certain thickness, accompanied by significant volumetric dilatancy. In the triaxial unloading creep tests, multistep unloading of the confining pressure was applied, while the axial pressure was kept constant. The results show that when the deviatoric stress is larger and the experienced creep time is longer, the unloading effect and creep characteristics become more apparent accompanied with obvious lateral dilatancy, eventually leading to significant creep–dilatancy. The progressive failure with time is caused by the damage accumulating with time-dependent crack expansion, which can be called as ‘time-dependent damage and fracturing’. The reasons for the above evolution process are presented, then the deformation mechanism of soft rock is revealed. The soft rock deformation mainly consists of two parts. One part is the pre-peak damage–dilatancy and post-peak fracture–bulking produced at the excavation unloading instant. The other part is creep–dilatancy caused by time-dependent damage and fracturing in a period of time after excavation. The above-mentioned results of damage, dilatancy and fractures evolution process are in good agreement with the in situ monitoring results and previous studies about the surrounding rock convergence, fracturing and EDZ (excavation damaged zone) development.

The present paper addresses the comparative study of two adjacent single-degree-of freedom structures for elastic and inelastic systems with and without pounding and also in the presence and absence of TMD under seismic excitations. The tuned mass damper considered for the present study is a passive device attached to single main structural unit in the form of weak storey at the top of main system. Total eight models have been considered depending upon the presence and absence of pounding as well as TMD in the analysis. The entire numerical simulation is carried out in time domain by considering the inputs of four real earthquake ground motions. An elastic adjacent structural system always overrates the pounding forces than the inelastic adjacent structural units. The use of TMD reduces the pounding forces in the adjacent structures. In pounding, structural displacement response is much sensitive for inelastic systems mostly under consideration or ignorance of TMD. Structural energy formation in the adjacent structures shows much variation with and without consideration of pounding as well as TMD.

One of the main concerns in an essential or highly important building is finding the appropriate structural system, while the efficiency of each conventional structural system varies in different cases. In this paper a new multi objective structural configuration is proposed and its efficiency for protecting buildings against the multi-hazards including earthquake, explosion and typhoon is shown in a case study of a 10 stories building sample. To create the optimum and efficient configuration of the structural elements, and to make some large spans, a configuration including Vierendeel girders is used. In this type of configuration, the inner suspended floor parts protect the outer elements by balancing perimeter span loads. This system makes a new condition for the building to be protected against the progressive collapse due to the terrorism attacks. Furthermore, the partially suspended floors in special stories act like tuned mass dampers (TMDs), which are suitable to decrease the amplitude of the displacement response of the structure during an earthquake.