Multi-criteria performance-based optimization of friction energy dissipation devices in RC frames

The effectiveness and the sensitivity of a Wireless impedance/Admittance Monitoring System (WiAMS) for the prompt damage diagnosis of two single-storey single-span Reinforced Concrete (RC) frames under cyclic loading is experimentally investigated. The geometrical and the reinforcement characteristics of the RC structural members of the frames represent typical old RC frame structure without consideration of seismic design criteria. The columns of the frames are vulnerable to shear failure under lateral load due to their low height-to-depth ratio and insufficient transverse reinforcement. The proposed Structural Health Monitoring (SHM) system comprises of specially manufactured autonomous portable devices that acquire the in-situ voltage frequency responses of a network of twenty piezoelectric transducers mounted to the RC frames. Measurements of external and internal small-sized piezoelectric patches are utilized for damage localization and assessment at various and increased damage levels as the magnitude of the imposed lateral cycle deformations increases. A bare RC frame and a strengthened one using a pair of steel crossed tension-ties (X-bracing) have been tested in order to check the sensitivity of the developed WiAMS in different structural conditions since crack propagation, damage locations and failure mode of the examined frames vary. Indeed, the imposed loading caused brittle shear failure to the column of the bare frame and the formation of plastic hinges at the beam ends of the X-braced frame. Test results highlighted the ability of the proposed SHM to identify incipient damages due to concrete cracking and steel yielding since promising early indication of the forthcoming critical failures before any visible sign has been obtained.

Objective The aim of this study was to evaluate the role of multicriteria optimization (MCO) in planning of intensity-modulated radiotherapy (IMRT).Methods Twenty IMRT patients (ten with prostate and ten with lung cancers) were randomly selected.For these patients,the treatment plans were designed with direct machine parameter optimization (DMPO).Based on these plans,new plans were designed with MCO,while keeping the setting conditions unchanged.Comparison was made between the two plans including the dose distribution,the dose volume histogram,the time of optimization and number of monitor unit (MU),but were play by pairing-t test.Results The plan designed in both optimizations satisfied all clinical requirements.For the same or better target coverage,rectum,bladder and small bowel were better with MCO compared with DMPO,MCO reduced 58％ of the time for optimization by average while MU increased 32％ by average for prostate cancer.For lung cancer,the whole lung,heart and spinal cord were better with MCO compared with DMPO,MCO reduced 59％ of the time for optimization by average while MU increased 11％ by average.Conclusions In comparison with DMPO,MCO reduces the dose of organs at risk,shorten the time of optimization. Key words: Multicriteria optimization; Direct machine parameter optimization; Intensity-modulated radiotherapy planning

Different types of gas reservoir such as Liquid Natural Gas (LNG) are among the strategic infrastructures, and have great importance for any government or their private owners. To keep the tank and its contents safe during earthquakes especially if the contents are of hazardous or flammable materials; using seismic protection systems such as base isolator can be considered as an effective solution. However, the major deficiency of this system can be the large deformation in the isolation level which may lead to the failure of bearing system. In this paper, as a solution, the efficacy of an optimally designed combined vibration control system, the combined laminated rubber isolator and rotational friction damper, is investigated to evaluate the enhancement of an existing metal tank response under both far- and near-field earthquakes. Responses like impulsive and convective accelerations, base shear, and sloshing height are studied herein. The probabilistic framework is used to consider the uncertainties in the structural modeling, as well as record-to-record variability. Due to the high calculation cost of probabilistic methods, a simplified structural model is used. By using theMont-Carlo simulation approach, it is revealed that this combined isolation system is a highly reliable system which provides considerable enhancement in the performance of reservoir, not only leads to the reduction of probability of catastrophic failure of the tank but also decrease the reservoir damage during the earthquake.Moreover, the relative displacement of the isolation level is controlled very well by this combined system.

The early phase of design contains multiple sources of unexpected circumstances which include the change or addition of performance requirements or design conditions with the process of the design phases. Therefore, designers are required to design considering those unexpected circumstances in the after phases. Previously, we proposed a preference set-based design (PSD) method, which obtains a unique design solution set from a point of view of design preference and robustness under various sources of uncertainties while incorporating the designer's preference in the early phase of design. PSD method represents the uncertain design information as the interval set. This paper proposes a new design method based on PSD method which can obtain diverse possible design solution sets for unexpected circumstances by deriving the multiple feasible design domains which satisfy the required performances. Obtaining diverse possible design solution sets could deal with the unexpected circumstances by selecting the optimal design solution from obtained diverse possible design solution sets in the early phase. In this paper, the proposed design method is applied to the design problem of an active isolation system of 4-story building to correspond to the additional unexpected earthquake ground motion which the designer cannot consider at the early phase of design.

The railway bridge damping tenon device can not only provide lateral, longitudinal and vertical stiffness, which means that the displacement of main beam will be effectively limited under earthquakes. The energy dissipation system formed by shock-absorbing bearing-damping tenon also has significant energy consumption performance, which can meet the seismic demand of the bridge in the high seismic intensity zone of the southwest mountainous area. However, the gap and yield force of the damping tenon and the design parameters of shock-absorbing bearing have a significant impact on the seismic isolation effect and on the limitation of the main beam displacement. Therefore, this paper takes the typical high-speed railway bridge in the southwest mountainous near-fault zones as research object, and a refined finite element analysis model of the bridge system considering the nonlinear dynamic coupling effects such as geometry, material and contact is established to study the most suitable design parameters of damping tenon. In general, the shock absorption rate of the pier bottom bending moment increases with the increases of the tenon’s gap and decreases with the increase of the tenon’s yield force. However, the determination of the damping tenon’s design parameters requires a comprehensive consideration of displacement limitation of the main beam. The research results can provide a basis for the optimization design of railway bridge damping tenon device in the future.

This paper focuses on the seismic protection of slender old masonry structures by the implementation of prestressing devices at key locations. The devices are vertically and externally located inside the towers in order to be reversible and calibrated. An extensive parametric study on a selected slender tower is carried out based on more than 100 nonlinear static simulations aimed at investigating the impact of different parameters on the seismic performance: (i) different prestressing levels; (ii) shape memory alloy superelasticity and (iii) changes in prestressing-forces in all the stages of the analysis until failure and masonry toe crushing. The tendon materials under analysis are conventional prestressing steel, fiber-reinforced polymers of different fibers and shape memory alloys. The parametric study serves to select the most suitable prestressing device and optimal prestressing level able to dissipate more earthquake energy. The seismic energy dissipation is evaluated by comparing the structural capacity curves in original state and retrofitte

Generally, in order to reduce the amount of calculations, engineers analyze and design the structures using simple force based methods such as quasi-static or spectral. However, we can use seismic risk assessment to study the damage due to probable earthquakes, instead of investigating force or displacement responses which are the basis of simple design methods. About the main purpose of this paper as a double criterion decision-making problem, it should be said that selecting the pylon shape is always a challenge in the design scheme of cable stayed-bridge. The construction costs of different shapes of pylons and the probable earthquake losses are the criteria of this problem. For the purpose of this paper, an example of a cable-stayed bridge is selected as the benchmark study. All the structural features remain the same, except the pylon which is designed in four different shapes. Then, the construction cost of the samples have been compared using a relatively analysis. For this purpose, the Incremental Dynamic Analysis (IDA) performed for the nonlinear models of the samples and IDA curves are obtained for the structure components. The fragility curves are obtainable for components by assigning the probabilistic seismic demand model to them and controlling the damage limit states. Then, based on an analytical method, the fragility curve for the bridge system is obtained from the components curve. Then the expected annual loss can be obtained for different pylon shapes by applying the loss ratio and hazard-recurrence relationship. Finally, the proper decision is made about the optimal pylon shape by applying the proposed Cost-Loss-Benefit method and defining a hybrid decision criterion. The final results of decision-making study indicate that the optimal pylon shapes for the studied span of cable-stayed bridge are in this order: H shape, Diamond shape, Y shape, and A shape.

Structures are designed in such a way that they behave in a nonlinear manner when subject to strong ground motions. Energy concepts have been widely used to evaluate the structural performance for the last few decades. Energy based design can be expressed as the balance of energy input and the energy dissipation capacity of the structure. New research is needed for multi degree of freedom systems (MDOFs)-real structures- within the framework of the energy based design methodology. In this paper, energy parameters are evaluated for low-, medium- and high-rise steel special concentrically braced frames (SCBFs) in terms of total energy input and hysteretic energy. Nonlinear dynamic time history analyses are carried out to assess the variation of energy terms along the height of the frames. A seismic energy demand spectrum is developed and hysteretic energy distributions within the frames are presented.

This study investigates the damage data after November 12, 2017, Iran earthquake (Mw 7.3), collected on 440 steel and reinforced concrete residential buildings. Structures have low-to-medium height and are located in Sarpol-e-zahab city, as well as in the west and northwest parts of Kermanshah province, Iran. The peak ground acceleration demands are determined according to data of the micro-shakemap of Sarpol-e-zahab city and the shakemap of Kermanshah province, while the mean values of intensities are determined from the existing empirical relationship between PGA and intensity. The investigated buildings are engineered steel and RC structures nominally erected according to the second and third editions of the Iranian code for earthquake-resistant buildings, but mostly under careless supervision and with low-quality materials. Damage probability matrix, vulnerability index and empirical fragility curves are presented for three subgroups of steel and RC structures on the basis of (i) structural materials and seismic resistant systems (i.e. braced, moment and combination of braced and moment steel frames, as well as moment and combination of moment and shear wall RC frames), without considering the height of structures; (ii) structural materials and height of structures, without considering the seismic resistant systems (i.e. low and medium-height steel and RC structures); (iii) structural materials, without considering the seismic resistant systems and height of structures (i.e. total data for steel and RC frames). The proposed fragility curves are compared with other fragility curves for steel and RC buildings from previous studies. Finally, since this earthquake was the first seismic event in Iran affecting a considerable number of steel and RC engineered buildings, the proposed empirical fragility curves are definitely unique and crucial for realistic damage and vulnerability assessment of similar buildings in future earthquake scenarios, as well as for developing rapid seismic loss assessment after damaging earthquakes.

Sustainable High-rises

Earthquake represents one of most destructive geological hazards. In this thesis I will attempt to understand it through controlled laboratory experiments. The earthquake dynamic rupturing process itself is a complicated phenomenon, involving dynamic friction, wave propagation, and heat production. Because controlled experiments can produce results without assumptions needed in theoretical and numerical analysis, the experimental method is thus advantageous over theoretical and numerical methods. Our laboratory fault is composed of carefully cut photoelastic polymer plates (Homalite-100, Polycarbonate) held together by uniaxial compression. As a unique unit of the experimental design, a controlled exploding wire technique provides the triggering mechanism of laboratory earthquakes. Three important components of real earthquakes (i.e., pre-existing fault, tectonic loading, and triggering mechanism) correspond to and are simulated by frictional contact, uniaxial compression, and the exploding wire technique. Dynamic rupturing processes are visualized using the photoelastic method and are recorded via a high-speed camera. Our experimental methodology, which is full-field, in situ, and non-intrusive, has better control and diagnostic capacity compared to other existing experimental methods. Using this experimental approach, we have investigated several problems: dynamics of earthquake faulting occurring along homogeneous faults separating identical materials, earthquake faulting along inhomogeneous faults separating materials with different wave speeds, and earthquake faulting along faults with a finite low wave speed fault core. We have observed supershear ruptures, rupture speed transition, directionality of rupture in faults with a material contrast, self-healing slip pulses in faults with a finite core, crack-like to pulse-like rupture transition in faults with a finite core.

The objective of this study was to propose methods for the optimal design of viscous or friction/hysteretic dampers in structures subjected to seismic and other dynamic loads. The systems investigated to control the dynamic response of the structure included passive linear viscous dampers, constant slip force friction dampers, and semi-active variable slip force friction dampers of the Off-On type. This work was primarily concerned with sizing of the viscous damper damping coefficients or the friction damper slip loads of the dampers at pre-selected locations within the structure. The dampers were considered to act in series with a flexible brace, as brace flexibility is an undesirable and often unavoidable characteristic. Two primary methodologies for the design were developed; one for the design of dampers in single degree of freedom (SDOF) structures using the transfer function concept, and one for the design of dampers in general multi degree of freedom (MDOF) structures based on linear quadratic control theory. It was found that the transfer function based technique proposed for the selection of optimal friction damper slip loads in SDOF structures provided insight into their design. While it was found that SDOF method could be extended to deal with MDOF structures, this process is limited to structures for which the distribution of dampers is known and calibrated to the SDOF design. As a basis for comparison, optimal friction damper slip loads and their distributions in a uniform 4-story structure were studied using an optimization procedure known as level set programming (LSP). The more general design method proposed based on structural control utilised the peak cycle control force and response quantities to estimate the optimal viscous damper damping coefficients approximating that of the fully active control. Then, considering the amount of energy dissipated in this peak cycle, estimates of the corresponding friction damper slip loads were obtained. Response spectral analysis (RSA) procedures, derived in state-space form, were used to incorporate the effects of earthquake excitation, while permitting the rapid evaluation of estimates of the peak cycle response quantities of non-classically damped structures. Reasonable agreement was obtained between the two methods. Three examples were provided to demonstrate the control theory based design method for MDOF structures; a uniform 4-story shear structure, a 2-D regular steel moment frame and 18DOF, 3-D eccentric building structure

Seepage criteria based optimal design of water retaining structures with reliability quantification utilizing surrogate model linked simulation-optimization approach

A general multidisciplinary procedure to approach the study of heritage building is synthesized in this PhD thesis considering the main features necessary to identify the structural behaviour of such type of buildings (historical inquires, geometric survey, material identification, in situ inquires) according to qualitative and quantitative methodologies. An in-depth survey has been carried out on the masonry of the Bell Tower of the “Santa Maria del Carmine” Church in the city of Naples, Italy. The analyses followed a multidisciplinary approach to identify its architectural and structural features, to identify the materials used and the state of damage and interventions made in various periods, to assess the stress state in the masonry under gravity loads, and to define its dynamic behavior. The information gathered represents the starting point for designing a seismic upgrade to meet the standards applied to historic monuments. A detailed historical, architectonical and structural inquires have been developed on the Bell Tower of “Santa Maria del Carmine” sited in Naples. These inquires have been preliminary to the study of the Tower by a finite element model for static and dynamic loads. The Bell Tower of “Santa Maria del Carmine” is an ancient (XVII century) historical masonry building located in city of Naples (Italy). The Tower is 68m high and is made by faced yellow tuff masonry along the initial 41 meters of height and by clay bricks along the upper levels. Internal and external walls are covered by decorative dark stone along the first nine meters. Geometrical and material surveys were performed to evaluate the actual damage state, the sequence of changes in the structures. Detailed experimental in situ investigations have been performed to define the geometry, to find the composing materials, to characterize their mechanical properties, to analyze damage condition and to identify the dynamic behaviour of the structure. The experimental results have been successively used to develop a numerical 3-D FE model. This model has been used to perform a linear static analysis under gravity loads to calibrate the mechanical parameters given by experimental results (i.e. the density of materials) and to check the safety condition for the vertical loads usually acting on the structure. Then, a linear dynamic analysis has been also accomplished to assess the values of Young’s modulus of materials and the constraint conditions offered by the surrounding buildings, based on parametric comparisons with the experimental results (natural frequencies and corresponding modal shapes obtained by dynamic in situ tests). This last study has been useful to understand the behaviour of the Tower under horizontal actions like an earthquake, considering that the structure is located in a medium risk seismic area. Therefore with the assumption of a ‘global behaviour’ of the Tower, a non linear static analysis (Push - over) was carried out based on the results of the previous inquiries, pointing out a low risk condition for the expected seismic actions (peak ground acceleration of 0.168g). Considering that previous numerical analysis evidenced that the Tower satisfied global checks for the expected seismic actions, in this paper attention is focussed on the study of local out-of-plane mechanisms activated by those actions. To prevent the activation of local mechanisms an innovative and low invasive intervention with FRP materials has been designed in the areas where local checks were not satisfying.

Efficiency is one of the important criteria for the design and evaluation of the construction quality. Power losses in planetary transmissions consist of losses in the gear contact, losses in bearings, losses in sealings, losses due to oil viscosity etc.The calculation of the gear transmission efficiency is generally confined to losses depending on friction on tooth sides, i.e. on the calculation of contact power losses. Nevertheless, it is not suitable for using efficiency as only criterion for optimal solution choice, but as a one of the set of criteria. The objective of this paper, is the application of multicriteria optimization to the planetary gear trains with efficiency as one of the criteria. Apart the determination of the set of the Pareto optimal solutions, the weighted coefficient method for choosing an optimal solution from this set is included in order to prioritize particular criterion.