Practice Periodical on Structural Design and Construction

This work is devoted to the study of the beam method in cylindrical shells from a mathematical point of view. We mainly focus on the methodological contribution by the engineer G. Kazinczy, well known by his influence on the Theory of Plasticity, in order to illustrate the structural calculation of long cylindrical reinforced concrete roof shells. Kazinczy’s methodological contribution to their structural calculation was developed at a time when attempts were being made to make computations in a rigorous manner, applying the mathematical mechanism of the theory of elasticity. The method is more feasible than the analytical method from the computational point of view, and it is based on the study of various states of equilibrium used by Kazinczy in his analysis of these structures.

The conventional buckling type of brace members offers lateral stiffness to the structural system; however, such members are likely to yield under tension and buckle under compression when loaded. Their unequal strength tends to produce higher demand on the framing system. Buckling-restrained braces (BRBs) offer excellent lateral force resistance, energy dissipation, and higher ductility thanks to their symmetrical hysteretic responses. The higher amount of friction, the gap between the core and restraining segment depending on the length, and the stoppers within the core segment are critical factors. This study investigates the effect of varying the yielding core length, the gap size between the steel core and the outer restraining segment, the position, and the frequency of stoppers on the hysteretic response of all-steel BRBs, considering the interaction between different parameters. Numerical analysis is performed with Abaqus finite-element software. A calibrated analytical model is used for the parametric study. The considered parameters are the cyclic behavior, axial resistance, energy dissipation capacity, compression strength adjustment factor, and strain hardening factor of the BRBs. Appropriate interface details are suggested based on the parametric finite-element analysis, considering the interactions among parameters. The study results reveal that the performance of BRBs with appropriate yielding core length, provided with sufficient gap size, is superior. Further, the selection of an appropriate gap size is of utmost importance. Finally, the provision of an increased number of stoppers enhances the performance of BRBs.

The present study proposes the use of base isolation for liquid containers and its effectiveness is investigated numerically. The seismic response of partially filled ground-supported rectangular tank with the submerged block is carried out under real earthquake ground motion. Six different earthquake ground excitations are considered, which are characterized as low-, intermediate-, and high-frequency-content earthquakes. The liquid domain is discretized as eight-noded isoparametric finite elements. The effect of variable height submerged block on sloshing response in the partially filled rectangular tank is investigated. Also, the effectiveness of base isolation in tank–submerged block systems is studied. The results of the parametric study imply that the laminated rubber bearings minimize the sloshing characteristics and thus improve the stability of the tank.

Because output accelerographs always contain noise, to use data in analysis and design of structures, there is a need for rational correction of raw data. These corrections include baseline correction, instrument correction, and filtration practices. In this paper, a 1-story steel moment frame and 3-story steel moment frame as benchmark have been used to study the effect of causal and acausal filtration. Accelerogram records have been used from five stations in successive earthquakes of Ahar-Varzaghan on August 11, 2012, and six stations that recorded the Sarpole-Zahab earthquake on November 12, 2017, for incremental dynamic analysis (IDA). The results show that the behavior of the representative structures by process of correction with causal and acausal filters in the elastic region, are roughly similar. Also the IDA summary curves show that the structures is subjected to higher intensity in acausal filters than in causal ones, so causal filtration in nonlinear analysis of low-rise structures seems to have more conservative responses in comparison with acausal one, not more than 15%.

Geopolymer concrete is a novel concrete that uses industrial wastes for its production process. The application of geopolymer concrete in construction is lower due to the dearth of sufficient information about the performance of structural elements with geopolymer concrete. A detailed experimental and numerical analysis was conducted to evaluate the flexural performance of ground granulated blast furnace slag (GGBS)-dolomite geopolymer concrete beams under cyclic loading. The effect of fibers on the performance of geopolymer concrete was studied by adding steel fibers in 0.25%, 0.50%, and 0.75% by volume of concrete. The behavior of geopolymer concrete beams, such as load-deflection characteristics, first crack load, ultimate load, ductility index, and crack pattern, were identified and compared with cement concrete beams. The ductility index was improved by 11%–44% with the addition of steel fibers at 0.25%–0.75% by volume of concrete. The cost to ultimate load ratio was 16% more in cement concrete than that of geopolymer concrete.

An experimental study on the structural behavior of steel-timber composite beams is presented in this paper. The timber beams were reinforced with flat and channel-shaped cold form steel (CFS) sections through different types of shear connectors (bolts, self-drilling screws, and epoxy glue). A total of nine beam specimens were tested under monotonic loading. The performance of the strengthened beams was evaluated on the basis of ultimate load-carrying capacity, flexural rigidity, energy ductility, and strength-to-weight ratios. The strengthening of beams with CFS sections delayed or prevented the typical brittle failure as observed in control beams. Among different types of shear connectors, epoxy glue proved to be the most reliable connection for the composite beam, whereas bolts were the least efficient. The use of channel sections leads to a considerable enhancement in the load-carrying capacity of the timber specimens by various mechanisms owing to synergetic effects between CFS and timber. Relative to the control beam, an appreciable improvement in structural efficiency and ductility index was observed for all the strengthened beams.

Experimental research was carried out regarding the flexural behavior under cyclic reversal loading of six full-scale external beam-column concrete joints cast with plain concrete in the presence of shear reinforcements in the joint regions. The types of shear reinforcements adopted in the joint region were horizontal stirrups and inclined bars. All specimens were designed to fail in the joint region. One had only one stirrup in the joint, another had five stirrups in the joint, and three joints had a fix through diagonal bars of diameters 10, 12, and 14 mm subsequently inserted in inclined holes of diameter 20 mm created in the joint region of the existing reinforced concrete (RC) frames, and the holes were filled with epoxy resin. The experimental results indicate that it is possible to increase the shear strength of joint regions with inclined bars. The increase in shear strength was proportional to the increase in the amount of the steel area of the inclined bars, and the overall performances were comparable in terms of strength to that of well-confined joints. From the analytical point of view, a simple model based on the limit state of concrete crushing with transverse stirrups and inclined bars in both the elastic and the yielded states was developed and verified against the experimental results.

This paper investigates the effect of flexibly attached secondary systems (FSS) on the dynamic behavior of primary structures (PS) under harmonic and seismic ground excitations. An FSS affects the main structure during ground excitation differently than a secondary system that is rigidly attached to it. Small displacements in the FSS are used to derive the equations of motion that define the behavior of the PS and FSS. The analytical formulation presented is validated by a finite element (FE) study conducted in SAP2000. The influence of mass ratio, tuning frequency ratio, and excitation frequency ratio on the dynamic behavior of the PS is investigated. The results show that the combined system (PS+FSS) behaves as a modified single degree of freedom (SDOF) structure at higher tuning frequency ratios. The dynamic response of the structure is independent of the mass ratio at low tuning frequency ratio of FSS. Under seismic excitations, the flexible structure’s response reduces considerably as the mass ratio increases, compared to a stiff structure at a higher tuning frequency ratio. When the tuning frequency ratio is equal to one, smaller mass ratios of FSS increase the seismic performance of the stiff structure. A design methodology is proposed to measure the spectral acceleration of the primary structure by incorporating the effect of FSS in the design response spectrum. An analysis of the tuning frequency ratio and mass ratio on the modified design spectrum is also presented. Finally, the proposed design methodology is validated with an existing study.

Equilibrium can be used to determine the geometric stability (kinematic determinacy) of a structure. For initial (conceptual) design, analyzing a structure’s equilibrium matrix first eliminates the added computational expense associated with performing a complete structural analysis if the design is determined to be unstable. This paper describes an economical procedure for ensuring the geometric stability of complex planar trusses using the equilibrium matrix and its transpose, the compatibility matrix, to support initial design. Equilibrium and compatibility matrices were derived for an individual truss member, and then the assembly process to produce the global equilibrium matrix (and global compatibility matrix) was demonstrated. Several examples illustrated the concepts, beginning with considering only the equilibrium of key joints (nodes) and progressing to formal analyses of the structure’s equilibrium and compatibility matrices using linear algebra. It was shown that structures can be simultaneously geometrically unstable (possessing one or more mechanisms) and statically indeterminate (possessing one or more states of self-stress). Analysis of a complex planar truss fully illustrated the utility of the procedure, and, by using the analysis results and associated visualization tools, strategies for rendering an unstable truss stable were presented.

This study investigates the effects of a submerged cylinder on the sloshing responses in a partially filled U-shaped container. The movable cylinder is placed at the horizontal portion of a U-shaped container, which can move along with the liquid. This study further investigates the vibration control capability of the system for long period structures under dynamic loads. Besides experimental study, to understand the dynamic characteristics of the system, numerical simulations are also carried out on an ANSYS version 18.0 (FLUENT) platform using a computational fluid dynamics (CFD) framework. The fluid flow inside the container is modeled using the volume of fluid (VOF) method. The variation of sloshing induced interface movement with the cylinder’s length and diameter is studied. It is found that an increase in the cylinder’s length or diameter increases the overall damping capability of the container. In addition, as a damper in reducing response of a single degree of freedom (SDOF) structural frame under harmonic and earthquake loads, the device shows great efficiency.

The studies on the seismic control of a secondary system (S-system) in the base-isolated primary system under multicomponent earthquake is scanty. In this study, an S-system response mounted on a floor of a three-dimensional (3D) base-isolated building is investigated under three component earthquake. The main objective of the study is to examine the response reductions of the S-system in all three directions, including the vertical direction, in which the building is not isolated. For the purpose of the study, two 6-story 3D building models, one base isolated and the other nonisolated, are analyzed. The S-system consists of a single portal frame with a mass at its center. The nonlinear time history analysis of both building models is carried out for three component ground motion, using commercial software SAP 2000, in order to study the control of response of the S-system. The nature, peak ground acceleration (PGA), and component ratios of the earthquake are varied to perform the parametric study. The findings of the study show that significant reduction in the lateral displacement and acceleration of the S-system is achieved by base isolating the building. In addition, the S-system’s vertical responses are reduced despite the isolation being ineffective in the vertical direction.

This paper presents a practical procedure based on a hybrid neural network-flexibility damage index technique to predict the severity level and location of damages in a gravity dam. Numerical models of the Beni-Haroun gravity dam in Algeria are elaborated and validated using ambient vibration tests. The measured frequency response functions are used to identify all the frequencies and mode shapes that can effectively be retrieved in order to limit the calculation of the flexibility matrix to these modes. Although the flexibility index is capable of capturing the damage signature in terms of location and severity, the extraction of such information, however, is difficult in most cases, particularly when reducing the number of degree of freedoms (DOFs) to those representing accessible positions of sensors on the downstream side of the dam. Hence, a feedforward neural network is trained using a database constituted of flexibility indices for numerically simulated damages. In the test phase, the neural network achieved 94% and 80% success in predicting the location and severity of the damage, respectively, showing the high potential of the hybrid method to be used in the practice of structural health monitoring.

Nowadays, steel shear walls are widely used as a seismic lateral resistant system all over the world. In this paper, a parametric study is presented to calculate the ratio of length to height ($L/H$) using numerical methods. Results show that $L/H=1.0$ has better performance than other ratios with respect to the absorbed energy, initial stiffness, and maximum considered load capacity. Therefore, it can be understood that the most significant effect of retrofitting with a steel shear wall (SSW) based on the maximum load capacity can be found in the model with $L/H=1.0$. Also, models with $L/H$ ratios of 1.33 and 1.50 have approximately the same increased load ratio. Finally, it can be concluded that changing the $L/H$ ratio does not affect the maximum load capacity and initial stiffness of a concrete frame without SSW. However, the $L/H$ ratio has an essential effect on the behavior of a concrete frame with SSW. The results show that the maximum load capacity is related to $L/H=1.5$ for the concrete frame with SSW. Finally, the nonlinear viscous damper was used to improve the performance of an SSW. Results show that the value of absorbed energy by two diagonal viscous dampers is higher than that of the chevron viscous damper. Therefore, two diagonal viscous dampers can damp more values of input energy during an earthquake and reduce the response of the structure.

This article aims to present the results of an investigation on detection and quantification of damage location and severity for steel structures using wavelet packet transform for denoising the initial signals, in combination with a peak picking technique, to capture the modal parameters of the structures. In the peak picking technique, as an extended version of the basic frequency domain method, modes can be identified from the spectral density when having a white noise input and a damped structural model. Using the spectral density matrix, this method estimates the modes by a singular value decomposing. Consequently, this decomposition results in a single-degree-of-freedom identification of the system for each singular value. In other words, in terms of a proposed two-step algorithm, the modal parameters of the structures are identified by decomposing their free vibration responses. Because the decomposed signal could has the same amount of energy as the main one, it can be utilized in the peak picking technique to obtain the modal parameters. In the next stage, the obtained modal parameters are compared with those obtained from auto-regressive moving average with eXogenous input (ARMAX) method to control the accuracy of the proposed methodology. Finally, the Minokowski method is employed to determine the structural damage intensity. Moreover, the precision of the proposed algorithm was measured against the results of a famous experimental benchmark structural model using modal characteristics.

Sheathed cold-formed steel (CFS) wall panels comprise studs, tracks, and sheathings on one side or both sides. It has been observed in the literature that sheathing contributes significantly to the axial load carrying capacity of CFS wall panels. Limited studies are available on comparing the efficacies of available design methodologies to evaluate the axial strength of CFS wall panels with sheathing. The present study investigates the efficacy of analytical/semianalytical methods, namely, the Rayleigh–Ritz (R–R) method and direct strength method (DSM), for evaluating the axial load carrying capacity of sheathed CFS panels. In DSM, three elastic buckling loads are evaluated, namely, local, distortional, and global, using an open-source finite strip method based software CUFSM version 4.05. The bracing provided by sheathing to the section is presumed as springs. For the first time, a problem is undertaken to verify the efficacy of both the mathematical models together to evaluate the axial load carrying capacity of sheathed CFS wall panels. The evaluated results by both the models are compared with experimental strengths of sheathed CFS wall studs from the experimental database including the tests conducted by the authors. Results demonstrate that DSM may be used effectively for predicting axial strength of sheathed CFS wall panels, as a substantially lower coefficient of variation (CoV) is obtained for DSM, which is 0.1274, than the R–R method ($\mathrm{CoV}=0.1897$). DSM is suggested over the R–R method for evaluating the axial load carrying capacity of sheathed CFS wall studs as it better takes into account the local buckling and inelastic effects.

Optimization and deployment of control systems with multiple control devices incorporated into a structure is a daunting task. The optimum location of the control device is intrinsically connected to the design parameters of the control algorithm. The positioning technique should be effectively embedded in the control algorithm for efficient structural control employing semiactive control devices. This paper presents an acceleration-response-based adaptive (ARBA) algorithm entrenched with the device placement optimization algorithm. The summation of the overall acceleration response of each floor of the structure is considered as the performance criterion of the proposed control strategy. The versatility of this method stems from the fact that the MR damper control and position design algorithm can be developed and designed to meet the performance needs of the system. Only a 5-story steel frame is deliberated since the numerical simulation is followed with experimental verification of control systems on the shake table. From the results of the numerical simulation, it was concluded that the positions of MR dampers are closely linked to the output goal of the control strategy selected by the designer. Furthermore, the ARBA strategy’s configuration and corresponding structural control outperformed the benchmark controller. For various sets of ground movements, the numerical findings were experimentally tested on a shake table and compared to the corresponding passive control strategies. The findings showed that ARBA strategies outperformed uncontrolled and passive control strategies in mitigating the acceleration response of the structure and thereby enhancing the serviceability performance of the structure during dynamic excitations.

This paper presents a renovation strategy to upgrade the conventionally constructed chevron braced (both concentric and eccentric) steel frames in such a way that each set of the upgraded braces would uniquely display the characteristics of two simultaneously working eccentric braces at each story. The upgraded configuration of the chevron brace is termed here as a multilevel eccentric chevron (MLEC). Nonlinear numerical analysis was conducted to access the inelastic behavior of the braced frames under cyclic loading. The reduced deflection of beams, rectification of the sudden peaks in the hysteresis curves obtained for the initially concentric chevron braced frame, symmetric/balanced hysteresis curves obtained for the initially eccentric chevron braced frame, and the significant improvement in the plastic dissipation by the MLEC braced frames indicated toward the achievement of an excellent seismic behavior. The presented strategy would be very cost-effective, handy (ease of construction), least disruptive, and cause minimal structural intervention. This strategy was found to significantly improve both the strength and ductility of the conventionally constructed chevron braced frames.

This paper presents the results of statistical analyses on a database comprising 592 deep excavations in Shanghai soft clays from 1995 to 2018. First, the general trends and patterns over time are outlined for seven different excavation methods and seven types of earth-supporting systems. Then, the major design factors are characterized in a statistical manner. Based on analyses of the collected data, the frequency distributions of ${\delta }_{hm}/H_e$ data (${\delta }_{hm}$ = maximum lateral wall displacement; $H_e$ = final excavation depth) corresponding to each excavation method and each earth-supporting system are presented; furthermore, the correlations of ${\delta }_{hm}/H_e$ with the major design factors are explored. In this new database, 90% of ${\delta }_{hm}/H_e$ data featured magnitudes no more than 1.0%, which frequently lie within 0.10%–0.55%, indicating better performance than other databases worldwide. Via extensive comparisons, both the optimum construction method corresponding to each type of earth-supporting system and the optimum earth-supporting system corresponding to each excavation method for controlling excavation performance were determined. Last, the major design and construction defects as well as natural hazards pertaining to abnormally large ${\delta }_{hm}/H_e=1.01-7.27\%$ tracked at 23 individual excavations are identified and summarized. These include excessive excavation duration, long wall exposure lengths, retaining walls toed in soft muddy clays, overexcavation at deep levels, surcharges behind retaining walls, inadequate supporting system stiffness, and intense rainfall; among these factors, walls toed in soft muddy strata are shown to be detrimental to the performance of excavations. For a deep excavation that is to be carried out in sensitive clayey strata, safety redundancy can be enhanced substantially by accounting for the degradation of soil strengths due to construction disturbance and/or rainfall infiltration in design. The findings and lessons from this study will be useful to professionals worldwide in efficiently achieving cost-effective designs and/or making reliable evaluations regarding the performance of deep excavations in soft clays.

Carbon fiber–reinforced polymer (CFRP) composites are effectively and predominantly used for flexure strengthening of RC beams. Recently, new emerging composite materials known as galvanized steel mesh (GSM) sheets, which are comprised of unidirectional ultrahigh-strength steel wire meshes, are gaining considerable attention in strengthening applications. The main aim of this paper is to compare the test results of RC beams strengthened with medium-density GSM (MSM) and high-density (HSM) laminates with that of CFRP laminates. Accordingly, a total of six RC beams were strengthened in flexure with equivalent CFRP, MSM, and HSM laminates, in addition to two control unstrengthened beam specimens. All beam specimens were subjected to symmetrical monotonic loading testing, and strain data were recorded along with deflection at the beams midspan. Experimental results showed that HSM laminates enhanced the flexural strength, stiffness, cracking performance, energy absorption, and ductility of RC beams compared with CFRP and MSM laminates. In addition, flexural bond tests were conducted on prism samples to compare the bond behavior between each of the three laminates and concrete interface. The test results also showed that HSM laminates failed at higher attained load levels than CFRP and MSM laminates. Current design guidelines were also used to predict the nominal flexural capacity of the control and strengthened RC beams. The results showed that the predicted ultimate load is in good agreement with the experimental results and the difference was in the range of $0.4\%-4\%$, respectively. Therefore, it has been concluded that GSM laminates can be used as an effective composite material for flexural strengthening of RC beams.

Being in proximity of high-seismicity regions, Dubai and United Arab Emirates (UAE) in general are characterized by a high level of seismic hazard uncertainty. This study presents a seismic risk quantification for the existing building stock in Dubai. It provides the much needed and critical input toward enhanced seismic resilience and preparedness. Five archetype buildings ranging from 2 to 16 floors were meticulously modeled to represent the most common buildings stock. The seismic performance of the reference buildings was assessed using incremental dynamic analysis (IDA). The IDA was performed as per a methodology from current standards and far-field ground motion records. Fragility curves were developed for three damage states, namely Immediate Occupancy (IO), Life Safety (LS), and Collapse Prevention (CP). At the maximum considered earthquake (MCE) level, the economic losses due to structural damage were estimated based on accepted standard current values. Human losses and injuries were projected using a methodology from current standards. Finally, corresponding seismic risk maps were generated. The seismic risk maps illustrate that the estimated number of fatalities and major injuries at the MCE level is generally low.

The present study recommends a confining reinforcement mechanism, welded wire mesh (WWM), to enhance the performance of columns during seismic loading. Experimental studies were done on concrete columns confined by WWM and subjected to axial load and reverse cyclic lateral loading. Enhancement in the performance was noted in specimens with WWM with $3\times 3$ mesh size exhibiting 2.65 times the energy absorption and 73% more cyclic lateral load capacity in comparison with specimens with conventional confinement as stipulated in the Indian standard code.

This paper presents cost-effective guidelines for practicing engineers to design, evaluate, or review the structural design of the sulfur recovery unit (SRU) used in refineries. Extensive efforts have been made over the last few years to develop economical strategies for the process and mechanical design aspects. Limited work is available in practice dealing with structural design of SRUs. This paper bridges the gap and provides economical structural engineering methodologies that can be utilized in practice for the design of SRUs. The sulfur vessel supports are categorized into three systems. Numerical and approximate models are proposed to simplify the analysis and the loading mechanisms during operation and testing. Design examples are also provided for steel pipe racks and vessel support systems that are commonly used in the sulfur recovery units.

This article deals with the seismic performance evaluation of concrete gravity dams considering fluid–structure–soil interaction in a finite-element framework. Two-dimensional finite-element formulation and analysis of dam–reservoir–foundation system was carried out in MATLAB code. A displacement-based Lagrangian technique was adopted for the dam and foundation domain, and the reservoir domain was modeled using the pressure-based Eulerian technique. The fluid–structure–soil interaction problem was solved using a direct coupling methodology. The coupled system consisted of three domains: dam, reservoir, and foundation. Free vibration analysis was performed to observe the effect of the interaction with the reservoir and foundation on the natural vibration modes of the dam. Dynamic response quantities of the dam, such as crest displacement and principal stresses at heel and neck were obtained considering interaction with and without the reservoir and foundation. The alteration in the responses of the reservoir and foundation based on the interaction with other domains was also examined. Emphasis was placed on the variation of the dynamic behavior of the dam, reservoir, and foundation when considered in a coupled manner. Finally, the seismic performance of concrete gravity dams was evaluated following a rational methodology based on the outcome of linear time history analysis. This study considered all the necessary modeling and analysis aspects to represent the actual physical scenario of the dynamic behavior of concrete gravity dams, and it provides a descriptive presentation of a simple and efficient approach for seismic safety assessment.

The 247-m DaShiXia (DSX) concrete-faced sand-gravel dam (CFSGD) is currently the highest structure of its type under construction in the world. By reviewing the specific conditions of this dam and common problems that have occurred in other comparable cases, this paper analyzes the technical issues that undermine the safety of the dam. Measures for controlling dam deformation and seepage, improving its aseismic performance, and reinforcing its concrete slabs are explained with the aid of experimental and numerical results and previous experience. The results of the analysis demonstrate that the deformation of the dam under static and dynamic loads is within the range of existing successful cases, thus providing fundamental confidence that the design is feasible. The use of L-shaped drainage within the dam is emphasized because of the vulnerability of sand and gravel material to seepage erosion, uncertainties in the results obtained from laboratory seepage tests, and the need to lower the phreatic surface. Numerical results show that the acceleration response is strong within the upper 4/5 part of the dam, which leads to confined aseismic measures within this particular portion. Reinforcing schemes for concrete-faced slabs and their joints are outlined, and some special design features, including the use of a high toe retaining wall, a stepwise toe plinth, and a deep empty tunnel in this dam, are also explained. The measures adopted are expected to result in acceptable performance of the dam and its impermeable system.

The rapid adoption of building information modeling (BIM) in the fields of architecture, engineering, and construction (AEC) has brought new and emerging challenges for collaborative practices related to the significant amount of BIM data that must be managed and controlled. This study formulated a cloud-based BIM governance framework focusing on data management for collaborative practices with BIM in AEC organizations. The framework is composed of three major constructs: (1) data sharing and integration uses in BIM, in the cloud, and with communication; (2) collaborative team practices with members, with teams, and for goal commitments; and (3) data governance with respect to access, control, policies, and contracts. A survey among a broad spectrum of BIM and virtual design construction (VDC) practitioners from major AEC organizations in the United States was conducted to explore the validity of the constructs. The framework served as an instrument to identify the level of implementation of cloud-based BIM governance within construction industry professionals. The results revealed factors that require attention to enable successful and collaborative BIM operations using cloud computing infrastructure. The factors highlighted requirements for governing the collaboration process and management of data, paving the way for adopting better solutions using cloud computing platforms in BIM collaborative practices.

In the present study, an innovative sacrificial system, comprising hollow tubes, for resisting blast load, is analyzed on a RC panel using the three-dimensional (3D) nonlinear finite-element software ABAQUS/Explicit. A square RC panel is modeled, and hollow mild steel tubes are used with a steel sheet to protect it from the blast loading. Blast load is applied through the ConWep program developed by the US Army. The Johnson-Cook (J-C) plasticity model with failure criterion is used to model the stress-strain response of mild steel and reinforcement bars under high strain rate loading. A Concrete Damage Plasticity (CDP) material model is used to model the behavior of concrete under blast load. Parametric studies have been performed considering different lengths ($L$), outer diameter ($D$), and thickness ($t$) of hollow mild steel tubes under varying blast loads. From numerical simulation results, it is observed that thinner sections of hollow mild steel tubes, in the proposed sacrificial system, performed better than the thicker sections. Further, it is observed that steel sheets can withstand a specific intensity of blast load governed by its thicknesses in the considered sacrificial system. The optimized combination of steel sheets and hollow metal tubes, in the considered sacrificial system, can reduce the peak deflection of the RC panel by more than 80%.

Recently developed steel self-centering moment-resisting frames (SC-MRFs) have been validated analytically and experimentally as having the potential to eliminate structural damage under a design basis earthquake and restore their original vertical position following a major earthquake. This study developed the repairability index of posttensioned self-centering frames for near-field earthquakes (RIPSCF-N). According to the 12 models of the studied building, which was a building that can be repaired, the maximum rotation in its connection after the earthquake did not exceed the rotation of the immediate occupancy performance. Based on this, the output data of incremental dynamic analysis (IDA) analyses were drawn according to the connection of relative rotation and spectral acceleration. According to the performance levels predicted in the literature for each acceleration level, the value of the connection opening is divided by the opening of the design basis earthquake (DBE) level. The resulting curve shows the repairability index according to spectral acceleration; if the index is less than 1, the repairability target is achieved. To evaluate the damage of angles, the angle failure probability of posttensioned self-centering frames for near-field earthquakes (AFPPSCF-N) was developed. This index equation is determined according to the fragility curve and the intensity of damage in each building. According to the RIPSCF-N, the nine-story buildings had lower repairability than the three-story buildings. According to result of the AFPPSCF-N, this indicates a higher percentage of angle damage in nine-story buildings than in three-story buildings at similar spectral accelerations.

The Illinois Department of Transportation (IDOT) will handle many upcoming projects due to the recent statewide infrastructure strategic plan and the fast-track efforts affecting many infrastructure projects amid COVID-19. Nevertheless, many change orders are anticipated to occur on IDOT’s projects. Thus, this paper examines the proper contractual management of changes within IDOT infrastructure transportation projects by following a research method based on the integration between a desktop analysis and a focus group analysis. The desktop analysis involved collecting information and data from existing resources, case studies, and documents related to change orders. The focus group analysis involved consulting with change order experts to verify that the outcome of each research step is useful and to validate the final outcomes of the paper. Based on 50 documented major change orders in IDOT projects and three litigated cases, two findings are provided. First, the top causes for key change orders within IDOT projects include contract administration, allowable contingencies, quantity omission or error, differing site conditions, and design changes. Second, the most critical change order related challenges within IDOT’s infrastructure projects include approval procedures, compensation considerations, and applicable laws. This paper offers flowcharts, synopsis of opportunities and risks, and a checklist to help the contracting parties better administer change orders. Ultimately, the contributions of this paper to the practice include: (1) minimizing the number and amount of change orders, (2) helping the contracting parties better understand how their individual responsibilities contribute to the proper processing and management of changes and variations, (3) offering contractors the ability to visualize the different steps involved in the approval of change orders, (4) assisting the project stakeholders in identifying change order-related areas for improvement, and (5) allowing project owners to better mitigate, manage, and administer the contractual aspects of change orders.

This paper aims to present a comparative study of dynamic response of a machine foundation supporting gas-lift reciprocating compressor using a conventional lumped parameter method and an FEM-based approach. Evaluation of dynamic response of machine foundation involves dynamic analysis of a rigid body supported on elastic half-space (soil mass). In general, conventional approaches involve idealization of the machine-foundation system as a rigid body and soil mass as a set of frequency independent (or dependent) elastic springs. However, for a foundation supporting large reciprocating machinery subjected to unusually high dynamic unbalanced loads acting at a significant height and foundation mat supporting several numbers of relatively flexible pedestals, due importance shall be attributed to the actual behavior of the machine-foundation system considering the soil-foundation interaction as well as the effect of boundary conditions. It is therefore necessary to substantiate the analysis result of conventional method with an alternative approach. As a part of the assessment of acceptability of lumped parameter output, i.e., natural frequencies and response amplitudes, a finite-element method–based approach was adopted. ANSYS (version 17) software was employed to create three-dimensional (3D) finite-element model where, apart from modeling the foundation-machine mass, soil layers were also modeled to include the kinematic and inertial interactions to simulate the real behavior of soil-foundation interaction as precisely as possible. Output results from both approaches were critically compared for all relevant parameters. This study indicates meaningful correlation among results obtained from both approaches in terms of amplitudes of vibration and natural frequencies of the foundation. For the governing coupled rocking-sliding mode, amplitude of vibration using conventional lumped parameter approach is obtained as 74.17 μm while the FEM approach results in an amplitude of 72.90 μm, indicating a difference of less than 2%. The frequency response curve, i.e., plot of variation of amplitude over a range of frequencies also reflects a significant amount of similarity in terms of maximum amplitude of response. The study also highlights the effect of soil improvement on the dynamic response.

This paper presents a practical design of machine foundation subjected to varying harmonic loads. The dynamic analysis of machine foundation is performed using an analytical method. The varying harmonic loads are generated by varying the speed of the machine as per the performance requirements of the plant, which essentially results in operating the machine at or near the resonance. The vertical vibration and coupled horizontal and rocking vibrations are represented using Lysmer’s and Hall’s analogs, respectively. The equations of motions are formulated considering the vertical motion and coupled horizontal and rocking motion of the foundation soil system in the lumped parameter approach. The analytical formulation is capable of considering the moments generated due to the eccentricity of loads (i.e., static weights of the machine and foundation). A computer program is developed using FORTRAN to obtain the practical solutions for the machine foundation soil system. The maximum amplitudes of the vertical and horizontal displacements of the case study example are 22.5 and 110.68 μm, respectively, for the operating frequencies ranging from 2.5 to 12.1 Hz. The performance of the induced draught fan foundation is evaluated using the General Machinery Vibration Severity Chart, the guidelines given in the publication Foundations for Machines: Analysis and Design, and the American Concrete Institute standard ACI 351.3R-04. These charts and guidelines help in assessing the performance of the machine foundation system during operation of the plant. Based on the results, the performance of the machine foundation system is rated as “good” to “very good” and “fair” to “slightly rough” category based on the obtained vertical and horizontal amplitudes of the displacements respectively. Based on the measured data, it is noted that the evaluated performance parameters are well within the operating parameters of the machine foundation system.