Effect of Coarse Aggregate Size on and Crack Opening in Normal and Relationship between Stress High Strength Concretes

Fine and coarse aggregates play an important role in the fracture of concrete. However, quantitative information available on the effect of the coarse aggregate size on the fracture properties of concrete is still limited. In the present paper, the effect of coarse aggregate size （single grade of 5～10, 10～16, 16～20 and 20～25 mm） on stress-crack opening （σ-w） relation in normal and high strength concretes （compressive strength of 40 and 80 MPa, respectively） was studied. The investigation was based on three-point bending tests implemented by fictitious crack analysis. The result shows that coarse aggregate size and cement matrix strength significantly influence the shape of σ-w curve. For a given total aggregate content, in normal strength concrete, smaller size of aggregate leads to a high tensile strength and a sharp stress drop after the peak stress. The smaller the coarse aggregate, the steeper the σ-w curve. By contrast, in high strength concrete, the effect of aggregate size on σ-w relation almost vanishes. A similar σ-w relation is obtained for the concrete except for the case of 20～25 mm coarse aggregate size. The stress drop after the peak stress is more significant for high strength concrete than that for normal strength concrete. Meanwhile, the smaller the coarse aggregate size, the higher the flexural strength. Fracture energy and characteristic length increase with increasing coarse aggregate size in both normal and high strength concretes.

Impact pressure of debris flow on beam dam

The use of open-type check dams in mountainous areas has become common practice in order to mitigate the effects of debris flow and extend the service life of engineering structures.The beam dam,a common debris flow control system,has received less attention in research on the impact process of debris flow and check dams compared to solid check dams.Additionally,the estimation of impact pressure in debris flow primarily considers debris flow characteristics,without taking into account the influence of geometric characteristics of the transmission structure.To better understand the impact process of debris flow on beam dams,a series of small-scale debris flow impact tests were conducted in a model flume.Key parameters,including velocity,depth,and impact pressure,were measured.The results show that the maximum impact pressure of debris flow is affected by both the characteristics of the debris flow and the relative opening size of the beam dam.Due to flow and edge occlusion in the middle of the beam dam,the discharge of debris flow is enhanced,resulting in a longer impact process and higher maximum impact pressure.Based on these findings,a calculation model of the maximum impact pressure of debris flow at the midpoint of the middle beam is proposed,which can be used to estimate the impact of debris flow on the discharge part of the beam dam.

A Straightforward Direct Traction Boundary Integral Method for Two-Dimensional Crack Problems Simulation of Linear Elastic Materials

This paper presents a direct traction boundary integral equation method(DTBIEM)for two-dimensional crack problems of materials.The traction boundary integral equation was collocated on both the external boundary and either side of the crack surfaces.The displacements and tractions were used as unknowns on the external boundary,while the relative crack opening displacement(RCOD)was chosen as unknowns on either side of crack surfaces to keep the single-domain merit.Only one side of the crack surfaces was concerned and needed to be discretized,thus the proposed method resulted in a smaller system of algebraic equations compared with the dual boundary element method(DBEM).A new set of crack-tip shape functions was constructed to represent the strain field singularity exactly,and the SIFs were evaluated by the extrapolation of the RCOD.Numerical examples for both straight and curved cracks are given to validate the accuracy and efficiency of the presented method.

Improving Extraction of Chinese Open Relations Using Pre-trained Language Model and Knowledge Enhancement

Open Relation Extraction(ORE)is a task of extracting semantic relations from a text document.Current ORE systems have significantly improved their efficiency in obtaining Chinese relations,when compared with conventional systems which heavily depend on feature engineering or syntactic parsing.However,the ORE systems do not use robust neural networks such as pre-trained language models to take advantage of large-scale unstructured data effectively.In respons to this issue,a new system entitled Chinese Open Relation Extraction with Knowledge Enhancement(CORE-KE)is presented in this paper.The CORE-KE system employs a pre-trained language model(with the support of a Bidirectional Long Short-Term Memory(BiLSTM)layer and a Masked Conditional Random Field(Masked CRF)layer)on unstructured data in order to improve Chinese open relation extraction.Entity descriptions in Wikidata and additional knowledge(in terms of triple facts)extracted from Chinese ORE datasets are used to fine-tune the pre-trained language model.In addition,syntactic features are further adopted in the training stage of the CORE-KE system for knowledge enhancement.Experimental results of the CORE-KE system on two large-scale datasets of open Chinese entities and relations demonstrate that the CORE-KE system is superior to other ORE systems.The F1-scores of the CORE-KE system on the two datasets have given a relative improvement of 20.1%and 1.3%,when compared with benchmark ORE systems,respectively.The source code is available at https:/github.COm/cjwen15/CORE-KE.

Open to Trade China-South Africa trade relations are alive with possibilities

In recent years, economic and trade relations between China and Africa have seen rapid development. As Africa’s largest trading partner, China’s trade relations with South Africa, the continent’s most potent economy, are an integral part of this