Dynamic ultimate strength analysis of stiffened plate based on Idealized Structural Unit Method

Marine and offshore structures are subjected to dynamic loads during the lifetime. The values or directions of dynamic loads rapidly change in time, causing a significant rise of inertial forces in structural elements. Dynamic loads appear as result of ship’s movement at sea, wind and wave acting, machinery operation, hull vibration and sometimes even as result of collision or explosion. The corresponding dynamic forces and moments act on the ship hull provoking the appearance of stresses, often leading to buckling, plastic deformations or fatigue cracks of the structural members. To ensure the safety and reliability of structures under dynamic loading it is necessary to estimate the transient effects on the collapse behavior of plate panels. According to the Common Structural Rules (CSR) the safety of marine structures must be proved performing the hull girder ultimate strength check. As a possible tool for the ultimate strength analysis, the Finite Element Method (FEM) is widely spread among engineers. In spite of the great effectiveness, the transient Finite Element Analysis (FEA) remains very time consuming and sometimes difficult to accomplish well. Therefore, the formulation of the Idealized Structural Unit Method (ISUM) is extended for the dynamic collapse analysis of marine structures.

To address the frequent occurrence of rock burst disasters in areas with wide coal pillars during mining in the western mining area of China, the wide coal pillar area of the Tingnan coal mine in Shanxi Province was used as the research background. Theoretical analysis, numerical simulation, and field tests were used to establish the mechanical criterion and the energy criterion for the dynamic instability of wide coal pillars. The process and mechanism of wide coal pillar dynamic instability under dynamic and static load disturbances were revealed, and a wide coal pillar rock burst prevention and control scheme was proposed. The results indicated that when the load above a coal pillar reached the stress failure index and the energy failure index was met, the coal pillar reached the critical conditions for rock burst. With increasing static load, the stress, energy, and range of the plastic zone all showed increasing trends on both sides of the coal pillar. Under a given dynamic load, the stress and plastic zone range of the coal pillar significantly increased compared to those without a dynamic load. Under a given static load, the greater the dynamic load, the more likely the coal pillar was to undergo dynamic instability. The evolution of coal pillar dynamic instability was divided into three stages: energy accumulation, local instability, and dynamic instability. When the critical stress and energy conditions for coal pillar dynamic instability are exceeded, rock burst will occur. To reduce the static and dynamic loads of coal pillars, a rock burst prevention and control scheme of energy release and load reduction was proposed and applied onsite. The monitoring results showed that this control plan effectively reduced the stress of the coal pillar and the dynamic load generated by the fracture of the overlying rock layer, indicating safe mining in this area of wide coal pillars.

The stability control of surrounding rock for large or super-large section chamber is a difficult technical problem in deep mining condition. Based on the in-site geological conditions of Longgu coal mine, this paper used the dynamic module of FLAC3D to study the response characteristics of deep super-large section chamber under dynamic and static combined loading condition. Results showed that under the static loading condition, the maximum vertical stress, deformation and failure range are large, where the stress concentration coefficient is 1.64. The maximum roof-to-floor and two-sides deformations are 54.6 mm and 53.1 mm, respectively. Then, under the dynamic and static combined loading condition: (1) The influence of dynamic load frequency on the two-sides is more obvious; (2) The dynamic load amplitude has the greatest influence on the stress concentration degree, and the plastic failure tends to develop to the deeper; (3) With the dynamic load source distance increase, the response of surrounding rock is gradually attenuated. On this basis, empirical equations for each dynamic load conditions were obtained by using regression analysis method, and all correlation coefficients are greater than 0.99. This research provided reference for the supporting design of deep super-large section chamber under same or similar conditions.

An improved ISUM rectangular plate element taking account of post-ultimate strength behavior

Geosynthetic reinforced and pile-supported (GRPS) provide an economic and effective solution for embankments. To investigate the load-bearing mechanism of the GRPS embankment in loess, experimental and numerical studies under static and dynamic loading are carried out. The characteristics of soil arch effect and tensile membrane effect of GPRS embankment under static and dynamic loading are revealed by analyzing pile–soil stress ratio, tension of geogrid, and stress distribution of pile. The test results show that the pile–soil stress ratio under dynamic loading is reduced by 2.3 compared with static loading. In comparison to static load, the soil arching effect is attenuated under dynamic load, and the stronger the static load soil arching effect, the greater the degree of weakening under dynamic load. In addition, under dynamic loading, the tensioned membrane effect is still effective, but its enhancement is not as pronounced as under static loading. Furthermore, by using the finite element software, the numerical model is developed and validated with the experimental results. The parameter analysis of the load-bearing performance of the GRPS embankment is accomplished using the finite element model as well.

Dynamic fragmentation is one of the primary fracture types for rock mass in rock engineering. The dynamic fragmentation process and dynamic fragment size characteristics are important for the fragmentation optimization in field. Most researchers studied the fragmentation forming process via dynamic compression test using the traditional split Hopkinson pressure bar (SHPB) system, in which the multiple dynamic loading is generally applied on the rock specimen. However, the effect of the multiple loading on the dynamic rock fragmentation characteristics was rarely attempted. In this study, the momentum-trap system is used in SHPB to achieve the single dynamic compressive loading on the rock specimen. Westerly granite and Fangshan marble were chosen to investigate the effect of multiple dynamic compressive loading pulses on the fragmentation characteristics. During the dynamic loading, the fragmentation process was captured using the high-speed camera. The results show that under the specific loading rate, the multiple loading has no influence on measuring the dynamic compressive strength of rocks, but it was observed in the high-speed images that more fragments were produced in the multiple loading. Moreover, the failure mode of tested specimens under distinct compressive loading rates was examined. The results indicate that the fragmentized degree of rocks with single dynamic loading is less than that with multiple dynamic loading at a given loading rate. This trend is relatively obvious when the loading rate is lower. In addition, the D50 values of rocks with multiple dynamic loading are smaller than those with single dynamic loading. The fragment size distribution also indicates that the multiple loading pulses dominantly influence the produce and size distribution of the fine-grain fragment. Furthermore, the mean fragment size derived from Weibull distribution decreases as the loading rate increases. The multiple loading pulses could decrease the mean fragment size and generate more fine grains when comparing to the fragment size of rocks derived from the single loading pulse. Therefore, the multiple compressive loading may result in an inaccurate fragmentation size analysis, and the single dynamic compressive loading should be applied when evaluating the dynamic fragmentation efficiency of rocks.

A centrifuge model is developed to simulate sequential dynamic and static loadings with clear boundary conditions, aiming to comprehend the mechanical response of a cantilever-type retaining wall embedded into the soft rock. The model wall was made of steel tubular piles with a 2 m diameter and 25 mm thickness in a prototype scale under 50g. Wall retained height (H) and embedment depth (dr) into model soft rock (qu = 1.4 MPa) were 12 and 3 m, respectively. Sequential loadings (dynamic and static) were applied to the wall with dry and saturated backfill sand. It was found that the resilience of the wall created by the confinement of soft rock during the dynamic loading is a critical factor that controls the earth pressure and the dynamic and residual displacements of the wall, both during and after the dynamic loading and the static loading. Due to the resilience effect, an effective earth pressure ratio of more than the design active or even an at-rest pressure coefficient could be expected, especially after dynamic loading. However, a slight wall movement in the static loading and wall creep displacement after dynamic loading could reduce this resilience effect.

Understanding the behavior of neck muscles is essential to accurately simulate the human head-neck segment movement especially for low-speed motor vehicle crash situation. Some head-neck mathematical models were designed using neck muscle activation behavior in isometric contraction (static loading) as the properties of neck muscle activation. However, neck muscle activation pattern and strength capability may vary between static and dynamic loading. This study aimed to determine the differences between neck muscle activation level under static and dynamic loading. A neck strength test involving 22 human volunteers was conducted with two different tasks in extension and flexion direction with three different loads. The neck muscle activation level is determined through measuring the electromyography (EMG) responses of selected flexor and extensor muscles using surface bilateral electrode and recorded. The findings showed that neck muscle activation level was significantly greater in dynamic loading than static loading ([Formula: see text]). These implied that more efforts from neck muscles were required to resist against dynamic loading than static loading. Nonetheless, the differences in EMG activities between these two loading conditions progressively decreased when more loads were applied. This study has established an empirical model to describe the relationship between neck muscle activation level and force output for both loading condition in flexion and extension.

The optical fiber has been extensively used as a sensor in some special fields. Because the optical fiber exists crackles itself and also produce the micro-crack as well as local damage, the fatigue behavior of the optical fiber become the main problem we care about. This paper presents the experimental study on the fatigue performance of bare fiber under static, dynamic and cyclic load. The corresponding fatigue life index (Stress corrosion index) n can be obtained, which are 17.14, 11.83 and 5.88, respectively. The experiment data reveal that fatigue life index is related to loading mode and is treated as the indicator of crack propagation resistance of materials. Because dynamic and cyclic loads can induce additional damage, the fatigue life declines dramatically under the same stress levels.

Aging effect for the ultimate strength of offshore structure is studied in this paper. A frame model of offshore structure is used, which is simplified from an actual offshore structure of jacket type. As an aging effect, corrosion due to wave, wind, current, tide, etc is considered. The history of collapse and the ultimate strength of the frame model are analyzed by using the idealized structural unit method (ISUM), for the concentrated load such as collision by a ship or an iceberg, changing the angle of collision. The analyses are performed for the initial state in which the pipe members of the frame model have the original sizes, and for the deteriorated condition in which the members are corroded and their thicknesses are reduced.The collapse behaviors (collapse modes) and the characteristics are clarified for the above various conditions. They are different depending on the angle of the collision even if the location of collision is the same. They change with the reduction of thickness of the members due to corrosion. The ultimate strength decreases proportionally to the reduction of strength of the member which is the cause of the collapse of the model, if the collapse mode does not change. But, it is possible that the ultimate strength decreased largely, if the collapse mode changes due to corrosion. The reduction of strength of the member is almost proportional to the reduction of thickness of the member. The maximum and minimum ultimate strengths of the frame model after corrosion can be estimated, using the maximum and the minimum of the ratio of reduced thickness to the original thickness of all the members in the frame model.The next second report, the frame model very close to an actual offshore structure of jacket type will be used to verify widely the characteristics and the estimating method of the ultimate strength obtained in this study.

The surrounding rock of the deep-buried chamber contains high-ground stress and initial cracks. Under a dynamic load, cracks will develop and expand, leading to the fracture and collapse of the confining pressure. Therefore, it is essential to study the failure process of fissured surrounding rock under the joint action of static stress and a dynamic load. In this paper, samples with cracks are used to simulate the defective rock mass. Similar modeling tests and numerical simulation studies were carried out to reveal the damage process of cracked deep rock mass under dynamic disturbance and investigate the impact threshold of rock mass damage under a certain level of hydrostatic pressure. The model test investigated the damage behavior for specimens with double-prefabrication cracks under pressure from a dynamic–static coupling load. The influence of the mechanisms of the angle of a crack, the initial static pressure, and impact capacity on specimen damage was analyzed. It was perceived that, with an increase in the angle of the crack, the omen of specimen damage is less obvious, and the specimen is subjected to sudden damage. On this basis, the damage process of the specimen containing prefabricated cracks under combined dynamic and static loads is realized through numerical simulation, and tests verify the accuracy of the results. The analysis allowed us to come up with a variation rule for the single-disturbance energy threshold for specimens with a prefabricated crack angle and the initial static load level of the specimen containing double-prefabrication cracks. The study lays the foundation for the future analysis of any deep rock mass failure process under dynamic disturbance and the protection of a deeply buried chamber.

A machine for static and dynamic triaxial testing

This study aimed to evaluate peri-implant bone reactions to dynamic and static loads in a rat model. Two cylindrical titanium implants were placed in the left tibia diaphysis of 39 rats, which were divided into three groups: static load for 4 weeks (S4), static load for 8 weeks (S8), and static load for 4 weeks followed by dynamic load for 4 weeks (S4D4). All implants received a mechanical lateral load. After the experiment, the implants were extracted to determine the attachment strength around the bone and implant. The new bone formation and bone-to-implant contact were measured using plain and polarized light microscopy. Histologic tissue analysis revealed good contact between the bone and implant, and new bone formation around all implants. The S4D4 group had the greatest attachment strength, new bone formation, and complex collagen fiber orientation in the new bone tissue, compared with the other groups. No statistically significant differences in bone-to-implant contact were observed among the three groups. Applying dynamic and static loads to osseointegrated implants increased the amplification of new bone. The attachment strength was significantly improved when dynamic load was used for 4 weeks, compared with when static load was used.

Mesoscopic numerical simulation of dynamic size effect on the splitting-tensile strength of concrete

The aim of this paper is to give a brief overview of same field measuring techniques of soil properties under dynamic loading. Evaluation of determination of spring and dumper properties of dynamically loaded soil are presented. The methods of measuring basic parameters such as the spring constant and damping coefficient are given. The responses of the single mass system, supported by a linear spring and a viscous damper are investigated for vertical, sliding, rocking, and torsion vibrations. Dynamic plate loading tests are used for measuring soil properties in a wide range of independent variety of magnitudes of static and dynamic loads. Influences of static and dynamic loads on spring and damping behavior of soil are studied at the building site of Uglegorsk thermal power plant. For soil behavior of the embedded foundations the methods of analysis have been developed. The field method for determining properties of embedded plates under dynamic loads has performed on the sites with loam and sand. Free vertical and horizontal vibrations of the plates induced by the proper impact of mass. Experimental results of the dumping ratio and mass ratios measuring have shown.