Search

To mitigate the environmental impact induced by CO2 emissions and nonrenewable resource consumption, which are typically associated with Portland cement production, ground granulated blast furnace slags (GGBSs) are usually added to the cement. In this study, the stabilisation effect of alkali-activated GGBS on saline soil and the hydration products of alkali-activated GGBS were investigated by unconfined compressive strength tests and scanning electron microscopy, respectively. The results show that Ca(OH)2 and NaOH as alkaline activators for GGBS significantly improve the unconfined compressive strength of saline soils. This strength is also enhanced by Na2SO4; however, the increase is considerably less than that provided by Ca(OH)2 and NaOH. In contrast, Na2CO3 is not a suitable alkaline activator for GGBS and has no significant effect on the unconfined compressive strength of saline soils. The study results further show that the morphology of hydration products varies because of the different alkaline activators involved in the hydration reaction with GGBS in saline soils.

A series of unconfined compression tests were performed to investigate the influence of wheat straws on the unconfined compression strength for saline-alkaline soils and saline-alkaline soils mixed with cement. In unconfined compression tests, 20 groups of soil specimens were prepared at five different percentages of wheat straws content (i.e., 0.0%, 0.1%, 0.15%, 0.2%, and 0.25% by weight of saline-alkaline soils) and four different percentages of cement content (i.e., 0%, 3%, 6%, and 9% by weight of saline-alkaline soils), and unconfined compression tests were carried out after 3-, 7-, 14-, 28-, and 56-day curing periods. Test results indicated that the inclusion of wheat straws within saline-alkaline soils and saline-alkaline soils mixed with cement leads to an increase in the unconfined compressive strength of specimens and also changed the brittle behavior to a more ductile one for specimens. In addition, based on the results from unconfined compression tests, a formula for predicting the unconfined compression strength of specimens related to cement content, wheat straw content, curing periods, etc., was determined, and comparing with the results from unconfined compression tests, it had higher precision in predicting the unconfined compression strength of specimens.

For the postearthquake temporary prefabricated light-weight steel structure, the enclosure walls composed of prefabricated slender columns and prefabricated strip slabs were used in the structure, which were manufactured from construction waste, such as fragments of bricks and tiles, concrete fragments, and chippings of stones. In order to obtain more accurate seismic performance of enclosure walls, a full-scale two-story experimental model was built to be placed on a shake table. In the test, acceleration transducers were fixed to the enclosure walls and steel frame, which were used to obtain the maximum acceleration of the enclosure walls and steel frame as well as natural frequency of the experimental model subjected to the seismic signal including Kobe wave and El-Centro wave. Moreover, pull-on the rope displacement transducers fixed to the exterior walls parallel to the direction of vibration were used to obtain the story drifts. The results of the shake table test show that when the experimental model is subjected to earthquake with maximum acceleration, enclosure walls are not damaged, owing to flexible connection between the steel frame and enclosure walls. Earthquake reduces the stiffness of enclosure walls, and the natural frequency of the experimental model decreases with increasing maximum acceleration of the seismic signal. In addition, based on the acceleration amplification coefficient, the collaborative performance of the steel frame and enclosure wall is better. Besides, when the experimental model is subjected to earthquake with maximum acceleration, the maximum story drift angle is only 1/2615.

For a new type of postearthquake temporary prefabricated lightweight steel structure proposed in this paper, mainly composed of steel frame, prefabricated hanger slabs, prefabricated hanger columns, reinforced concrete superposed slabs, etc., parameters of dynamic property for the structure, including natural frequency, vibration mode, damping ratio, etc., are determined by the test method. For prefabricated hanger columns and prefabricated hanger slabs, they are all produced with construction waste in factory and assembled on-site, which can form exterior walls. The united method, based on forced vibration method and ambient random vibration method, can quickly obtain accurate natural frequencies of the full-scale two-story experimental model. In this paper, damping oscillatory method is used to obtain damping ratio which can be determined only by the test method. In order to analyse the modal of the experimental model, a finite element model for the full-scale two-story experimental model is established, where the weight of prefabricated hanger slabs is assumed to be supported by prefabricated hanger columns, and the stiffness of prefabricated hanger columns is also increased. In addition, the connections between lightweight steel frame and prefabricated hanger columns are regarded as flexible connection. Comparing natural frequencies obtained from the finite element method with that obtained from the test method, magnification factor of stiffness for prefabricated hanger column is determined. In the analysis of modal for the full-scale two-story experimental model, the results show that the experimental model satisfies the requirement of design for seismic performance.

A static loading test was carried out on a 1/3-scale concrete-filled square steel tubular column-steel beam frame (CFSTSBF) specimen with 2 spans to study its progressive collapse behaviors under the middle column failure scenario using the alternate load path method and to examine the failure mode and load transfer and main resistance mechanisms of the residual structure. Then, theoretical models of the specimen, involving the whole collapse process, were developed, and the resistance and deformation relationships of each model were calculated and validated with test results. The results indicated that the specimen collapse process includes the elastoplastic stage, plastic stage, transfer stage, and catenary stage, the beam mechanism and catenary mechanism were the principal mechanisms for the structure against progressive collapse, and catenary action can significantly strengthen structural resistance. The modified theoretical models with higher practical accuracy could be used to assess structural performances against progressive collapse.

In this paper, monotonic horizontal loading tests were carried out to study the bearing capacity of the cone-shaped foundation in marine fine sand. With load-controlled methods, the horizontal load was applied to the rod of cone-shaped foundation at loading eccentricity ratios of 5.0, 6.0, and 7.0. In addition, theoretical analysis was used to investigate the horizontal ultimate bearing capacity, and finite element analysis was also used in this paper to investigate the influence factors of the bearing capacity of cone-shaped foundation. Based on the theoretical analysis, the formula for horizontal ultimate bearing capacity was deduced. Test results show that, at the same loading eccentricity, cone-shaped foundation can provide higher H-M bearing capacity as well as lower lateral deflection compared to regular circular foundation for wind turbines. In addition, the deflection-hardening behavior of load-deflection curve for cone-shaped foundation is also observed. Numerical analysis results show that the H-M bearing capacity of the cone-shaped foundation increases with increasing aspect ratio and buried depth, however, and decreases with increasing loading eccentricity. Based on the results from finite element analyses, several equations to calculate the maximum moment bearing capacities are put forward, which take the aspect ratio, loading eccentricity, and embedded depth into account.

To study the interfacial bond-slip performance of concrete-filled square steel tubes (CFSSTs), taking the core concrete strength, slenderness ratio, and width-to-thickness ratio as the influencing factors; 9 specimens were designed with 3 factors and 3 levels for the orthogonal test method. In addition, different from the above 9 specimens, one specimen without rust removal was designed for the purpose of comparison. Based on the bond stress distribution and deformation coordination relationships between the specimens during the push-out tests, a theoretical formula for calculating the relative slip of a CFSST was deduced. The results show that with the increase of load, the relative slip at the loading ends was earlier than that at the free ends of the specimens; the interfacial bond failure and relative slip gradually developed from the two ends towards the centre of the specimens; the increase of the bond stress in the middle part was faster than that at the ends of the specimens. The order of these factors from main to secondary is the presence of rust in the inner wall of the square steel tube, the slenderness ratio, the core concrete strength, and the width-to-thickness ratio.

In order to assess the seismic performance of damaged reinforced concrete (RC) frame strengthened with carbon fiber reinforced polymers (CFRP) sheets, two experimental specimens with identical reinforcement ratio and geometric dimensions were designed following Chinese code for seismic design of buildings. Experimental specimens consist of a reference (undamaged) RC frame, namely, KJ-1, and an earthquake-damaged RC frame strengthened with CFRP sheets, namely, KJ-2. A pseudostatic test was conducted on the two specimens to simulate moderate earthquake damage. The strengthening effects of CFRP sheets on damaged RC frame were discussed in terms of hysteretic curve, skeleton curve, stiffness degradation, and ductility. In addition, numerical method based on fiber model method was utilized to analyze the seismic performance of KJ-1 and KJ-2 and it is compared with the experimental result. Both the results confirm that the method of exterior bonding CFRP sheets on the damaged RC frame has restored the seismic performance such as bearing capacity, stiffness, and ductility to its original undamaged level, and some of the seismic performance of the damaged RC frame strengthened with CFRP sheets is even better than the undamaged one, which proves that the method has significant effect in strengthening postearthquake-damaged RC frames.

This paper presents a deterministic SATQ-type mathematical model (including susceptible, alcoholism, treating, and quitting compartments) for the spread of alcoholism with two control strategies to gain insights into this increasingly concerned about health and social phenomenon. Some properties of the solutions to the model including positivity, existence and stability are analyzed. The optimal control strategies are derived by proposing an objective functional and using Pontryagin’s Maximum Principle. Numerical simulations are also conducted in the analytic results.

Abstract: Social media has become very popular nowadays by spreading plentiful human‐centric data to a large number of audience. A rich body of literature has studied the influence maximization problem in social networks under certain propagation models. However, existing models suffer from the assumption of unlimited propagation time and some of them are nondeterministic. Influence maximization algorithms within those frameworks are often trading off between performance guarantee and computational cost. In this paper, we try to formulate the influence maximization problem in another way, where we limit the propagation time to a predefined propagation round and in each round maintain the probability to make the propagation process more tractable. We introduce a new diffusion model called a probability propagation model and formulate this optimization problem as a holistic probability maximization problem. We show that information diffusion estimation in the proposed framework is not NP‐hard. Hence, any algorithm within it will be more efficient. However, the maximization problem is still NP‐hard. After proving the submodularity in the proposed framework, we design a partial‐updating greedy algorithm and its heuristic extension to solve the maximization problem. Extensive experiments on four synthetic data sets and four real‐world data sets from Facebook, Wikipedia, arXiv, and Epinions demonstrate the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]