Normalized strength reserve principle for variable amplitude fatigue life prediction of adhesively bonded aluminium joints/Normalisiertes Festigkeitsreserve-Prinzip für die Vorhersage der Lebensdauer von geklebten Aluminiumverbindungen bei variablen Lastamplituden

Over the last several decades, adhesive bonding has been validated as a good alternative to traditional joining methods in metallic construction. On the other hand, the main factor that limits the wider use of structural adhesives in civil engineering industry is scepticism about their long-term performance, especially when subjected to variable amplitude fatigue loading. Most of the research on predicting the fatigue life of adhesive joints subjected to this type of loading dealt with composite adherends. In this paper, straightforward method for prediction of strength degradation and fatigue failure under random spectrum loading is presented and validated for the case of adhesively bonded single lap joints made of aluminium adherends. It is based on the normalized strength reserve principle, proposed by the same authors in their previous research. The normalized strength reserve model is expanded to the case of variable amplitude fatigue, incorporating the cycle mix parameter in order to account for load interaction effects. Very good agreement was obtained between the fatigue life predictions of the presented method and experimental results from the literature.

Influence of Bitumen Type and Asphalt Mixture Composition on Low-Temperature Strength Properties According to Various Test Methods

In regions with low-temperatures, action transverse cracks can appear in asphalt pavements as a result of thermal stresses that exceed the fracture strength of materials used in asphalt layers. To better understand thermal cracking phenomenon, strength properties of different asphalt mixtures were investigated. Four test methods were used to assess the influence of bitumen type and mixture composition on tensile strength properties of asphalt mixtures: tensile strength was measured using the thermal stress restrained specimen test (TSRST) and the uniaxial tension stress test (UTST), flexural strength was measured using the bending beam test (BBT), and fracture toughness was measured using the semi-circular bending test (SCB). The strength reserve behavior of tested asphalt mixtures was assessed as well. The influence of cooling rate on the strength reserve was investigated and correlations between results from different test methods were also analyzed and discussed. It was observed that the type of bitumen was a factor of crucial importance to low-temperature properties of the tested asphalt concretes. This conclusion was valid for all test methods that were used. It was also observed that the level of cooling rate influenced the strength reserve and, in consequence, resistance to low-temperature cracking. It was concluded that reasonably good correlations were observed between strength results for the UTST, BBT, and SCB test methods.

Influence of Bitumen Type and Asphalt Mixture Composition on Low-temperature Strength Properties

In regions with low-temperature action transverse cracks can appear in asphalt pavements as a result of thermal stresses that exceed the fracture strength of materials used in asphalt layers. To better understand thermal cracking phenomenon, strength properties of different asphalt mixtures were investigated. Four test methods were used to assess the influence of bitumen type and mixture composition on tensile strength properties of asphalt mixtures: tensile strength using the Thermal Stress Restrained Specimen Test (TSRST) and the Uniaxial Tension Stress Test (UTST), flexural strength using the Bending Beam Test (BBT) and fracture toughness using the Semi-Circular Bending Test (SCB). The strength reserve behavior of tested asphalt mixtures was assessed as well. The influence of cooling rate on strength reserve was investigated and correlations between results from different test methods were also analyzed and discussed. It was observed that the type of bitumen is a factor of crucial importance to low-temperature properties of the tested asphalt concretes. This conclusion was proved by all test methods that were used. It was also observed that the level of cooling rate influences the strength reserve and, in consequence, resistance to low-temperature cracking. It was concluded that reasonably good correlations were observed between strength results for the UTST, BBT and SCB test methods.

THE EXPERIMENTAL ANALYSIS OF CAPTIVE ASSEMBLIES OF THE PANEL SYSTEM

The increase in the number of storeys is impossible without deviation from standard projects, where the structure of assemblies is not designed for buildings that have more than 12 storeys. That’s why it’s necessary to strengthen assemblies. For that purpose the testing of assemblies of the panel system, which is unique in modern textbooks on design, is performed. The paper presents the results of tests conducted at the plant ZHBI-Vostok of Chelyabinsk. The strength and stress-strain performance of an external horizontal assembly in two different versions (with slab-wall junction and without junction) is evaluated. As a result of experimental data processing, the effect of force eccentricity on the stress condition of assemblies is determined. This influence should be taken into consideration in case of hand calculations on assemblies. The axial and angular strain before the failure of assembly samples and the strength reserve of studied structures are specified.

On Strength Reserve Assessment for Prismatic Folded Plate Roof Structures

The paper presents the results of experimental studies and numerical simulation of straining and failure of reinforced concrete folded-plate roof structures in limit and out-of-limit states performed on models and real structures, taking into account the combined mechanical loads and environmental actions. The results of the study show that in the process of reconstruction design for concrete prismatic roof structures of operated industrial and public buildings, along with the traditional limit state methods of calculation it is reasonable to carry out a residual strength reserve analysis.

Research on the Dam Foundation Stability and Reinforcement Measures of the 12th Sluice Section of Xiangjiaba Hydropower Station

By two-dimensional nonlinear finite element strength reserve coefficient method and the rigid body limit equilibrium method respectively, a comprehensive study of the stability of the 12th sluice section of XiangJiaba hydropower station is made and some conclusions of the instability mode and the lack of safety are reached. The reinforcement measures, which set up concrete cogging at the dam heel and put up additional drainage holes at the stilling basin,are proposed and calculated by the strength reserve coefficient method and the rigid body limit equilibrium method respectively again,Results show that the dam foundation safety meets the code’s standards if the . reinforcement measures are adopted.

Research on a New Kind of Waterproof Agent for Desulphurization Gypsum Materials Block

The paper studied a compound desulphurization gypsum waterproof agent, which could modify the water-resistance performance of gypsum products on the basis of their microstructural properties. The waterproof mechanics were the synthesis results of superficial hydrophobic of hydrophobic emulsion, hindrance water of film forming matter and reducing the porosity in materials. The experiment results showed that the water-absorption rate of gypsum hardened body can be reduced to 3.5% and that the compressive strength reserve rate was 89.7% after 24h.