Pure Compression Loading Research Articles

A Study on the Compressive Behavior of Additively Manufactured AlSi10Mg Lattice Structures.

The mechanical behavior of the metallic components fabricated by additive manufacturing (AM) technologies can be influenced by adjustments in their microstructure or by using specially engineered geometries. Manipulating the topological features of the component, such as incorporating unit cells, enables the production of lighter metamaterials, such as lattice structures. This study investigates the mechanical behavior of lattice structures created from AlSi10Mg, which were produced using the laser beam powder bed fusion (LB-PBF) process. Specifically, their behavior under pure compressive loading has been numerically and experimentally investigated using ten different configurations. Experimental methods and finite element analysis (FEA) were used to investigate the behavior of body-centered cubic (BCC) lattice structures, specifically examining the effects of tapering the struts by varying their diameters at the endpoints (dend) and midpoints (dmid), as well as altering the height of the joint nodes (h). The unit cells were designed with varying parameters in such a way that dend is changed at three levels, while dmid and h are changed at two levels. Significant differences in Young's modulus, yield strength, and ultimate compressive strength between the various specimen configurations were observed both experimentally and numerically. The FEA underestimated the Young's modulus corresponding to the configurations with thinner struts in comparison to the higher values found experimentally. Conversely, the FEA overestimated the Young's modulus of those configurations with larger strut diameters with respect to the experimentally determined values. Additionally, the proposed FE method consistently underestimated the yield strength relative to the experimental values, with notable discrepancies in specific configurations.

Experimental study on debonding and buckling of externally bonded carbon fiber reinforced polymer sheets in compression

Although the compressive strength of Fiber Reinforced Polymer (FRP) sheets is neglected in the design of FRP-retrofitted Reinforced Concrete (RC) elements, they may be subjected to compressive stress in some load combinations. In the present study, an experimental study is conducted to investigate the behavior of externally bonded Carbon Fiber Reinforced Polymer (CFRP) sheets in compression. The experimental program is carried out in two phases. First, the behavior of CFRP strips bonded on concrete cylinders and subjected to pure compressive load is assessed. At this stage, the influence of concrete compressive strength, the dimensions of CFRP strips (thickness, width, and free length), and the type of adhesive used for bonding CFRP strips on the concrete surface, on the behavior of CFRP strips in compression are investigated. According to the test results, the FRP strips bonded with weak resin exhibit debonding failure and simultaneously buckle at a relatively low compressive strain, while CFRP strips bonded with stronger adhesive do not exhibit debonding failure in compression until concrete crushing. The behavior of CFRP strips bonded on reinforced concrete (RC) beams subjected to compressive stress due to bending moment is investigated in the second phase of this study. For this purpose, nine RC beams with the same dimensions and reinforcement detailing are fabricated and retrofitted using CFRP strips with different configurations. Four-point bending test is conducted at this stage of the experimental program. The results of the bending tests show that debonding failure and buckling of CFRP strips are observed in specimens with relatively thick CFRP sheets (3 and 4-layer) and larger free lengths.

Rate sensitive plasticity-based damage model for concrete under dynamic loading

In this manuscript, a rate-sensitive plasticity-based damage model for concrete subjected to dynamic loads is presented. The developed rate-sensitive damage model incorporates the key experimental evidence related to strain rate and damage rate. With increasing strain rates, the model is able to predict a decrease in the rate of damage evolution due to artificial stiffening effects together with a final higher level of damage. The major contribution of the work is to include the effect of damage rate, strain rate and also to consider all the physical mechanisms of damage. This is achieved by using a power law model to relate the rate of damage to the equivalent plastic strain rate. The damage parameter considers hydrostatic, tension and compression damage. Such a damage definition helps in the prediction of pulverized damage due to a loss in cohesive strength at increased hydrostatic stress, shear-induced compressive damage and tensile microcracking. Strong volumetric deformation of the material that includes hydrostatic and compaction damage is also considered in the model. Because hydrostatic damage accounts for the reduction in stiffness and compaction damage accounts for the increase in stiffness under pure compressive loading. A strain rate-dependent failure surface is considered and with increasing strain rate there is an increase in the size of the failure surface which is capped at an upper limiting value. The incremental effective stress-strain relationship is defined in terms of rate of damage, accumulated damage and viscosity parameters reflecting the inherent inertial, thermal and viscous mechanisms respectively. The stress-strain relationship in the model also accounts for stress reversals that occur due to interference of an incident and reflected wave, by including a Heaviside function. The developed model is implemented in LS-DYNA using vectorized UMAT. Verification, validation and parameterization of the developed model have been made through several numerical analyses.

On angular and surface interactions in two-dimensional elastic lattices

This paper deals with two-dimensional elastic lattices which asymptotically converge towards isotropic linear elastic continua. The square lattice composed of central and angular interactions, pioneered by Gazis et al. (1960) for 3D cubic lattices, allows the modelling of isotropic linear elastic continua (in the continuous asymptotic limit) with equivalent Poisson's ratios smaller than 1/3 in a plane stress assumption. This paper presents an alternative or complementary elastic model based on surface elastic interactions, which can be viewed as a complementary lattice model for values of Poisson's ratios greater than 1/3 in plane stress. The physical background of this non-central potential is discussed, basing on the existence of a dual surface pressure. The model can be also introduced from variational arguments. This surface model of Fuchs type is shown to be equivalent to a perimetric elastic model in the linear range. Additionally, this paper explores the possibility of coupling both surface and angular lattice elasticity for square lattices, with the potential to cover a large variety of elastic continua in the asymptotic limit. Gradient elasticity and lattice-based nonlocal elastic continua are constructed, starting from this simple square lattice composed of angular, surface and central interactions. The static behaviour of these square lattices (with central, angular and surface interaction) is investigated in pure compression and pure shear loading, with exact analytical solutions for the discrete displacement field.

Structural analysis of rack upright frames under a pure compression load by means of a nonlinear Generalized Beam Theory analysis

AbstractRack upright frames of conventional pallet racking systems are obtained by the assembly of uprights and braces or diagonals. Rack uprights are commonly mono‐symmetric open thin‐walled members with regular perforations along their length. These perforations are used to enable the connection with braces and beams by means of bolts or hooks. The structural behaviour of a rack upright frame under a pure compression load, in which the buckling phenomenon has a relevant influence, depends on several geometrical parameters, such as the column cross‐sectional dimensions, perforations characteristics, frame length, distance between braces, etc. Therefore, these particular issues should be considered to perform a proper structural analysis.In this paper, the structural behaviour of a pallet rack frame under a pure compression load is analysed by means of eigenbuckling and geometrically nonlinear Generalized Beam Theory (GBT) analyses. The influence of GBT deformation modes involved in the analysis is discussed. Moreover, different approaches to reproduce the connection between uprights and braces are presented and discussed. Finally, GBT results are compared with beam, shell finite element analysis and experimental values.

Structural Performance of Nanosilica-Blended Square and Circular CFST Stub Columns

The study focuses on the structural behavior of concrete-filled steel tubular (CFST) stub columns with conventional cement concrete and nano-silica blended (doses of 4%, 6%, 8%, and 10% nano-silica by weight) concrete core infill of M25 grade under a pure axial compressive load. The strength and deformation capacities, as well as failure modes, of the CFST columns were assessed with reference to steel hollow and reinforced concrete (RC) stub columns. At optimum replacement of cement with nano-silica, the increase in strength from filling the hollow steel columns is about 1.6 and 1.5 times for square and circular sections, respectively. The addition of 6% nano-silica to the cement concrete core of CFST columns showed 2.55 and 1.19 times more strength as compared to RC stub columns with square and circular sections, respectively. As a result, adding nano-silica to the concrete mix increases the core’s axial compressive load carrying capacity and strengthens the nano-silica blended CFST stub column. The addition of the optimum doses of nano-silica increases the higher rate of hydration and rapid formation of hydrated products in the cementitious matrix due to its higher specific surface area. Due to its higher specific surface area, adding the right amount of nano-silica speeds up the formation of hydrated products in the cementitious matrix and makes the rate of hydration faster.

Development, calibration and validation of a comprehensive customizable lumbar spine FE model for simulating fusion constructs.

Instrumentation alters the biomechanics of the spine, and therefore prediction of all output quantities that have critical influence post-surgically is significant for engineering models to aid in clinical predictions. Geometrical morphological finite element models can bring down the development time and cost of custom intact and instrumented models and thus aids in the better inference of biomechanics of surgical instrumentation on patient-specific diseased spine segments. A comprehensive hexahedral morphological lumbosacral finite element model is developed in this work to predict the range of motions, disc pressures, and facet contact forces of the intact and instrumented spine. Facet contact forces are needed to predict the impact of fusion surgeries on adjacent facet contacts in bending, axial rotation, and extension motions. Extensive validation in major physiological loading regimes of the pure moment, pure compression, and combined loading is undertaken. In vitro, experimental corridor results from six different studies reported in the literature are compared and the generated model had statistically significant comparable values with these studies. Flexion, extension and bending moment rotation curves of all segments of the developed model were favourable and within two separately established experimental corridor windows as well as recent simulation results. Axial torque moment rotation curves were comparable to in vitro results for four out of five lumbar functional units. The facet contact force results also agreed with in vitro experimental results. The current model is also computationally efficient with respect to contemporary models since it uses significantly smaller number of elements without losing the accuracy in terms of response prediction. This model can further be used for predicting the impact of different instrumentation techniques on the lumbar vertebral column.

Continuum modeling of nonlinear buckling behavior of CNT using variational asymptotic method and nonlinear FEA

Carbon nanotubes (CNTs) exhibit a unique buckling behavior due to their slender tubular geometry and thin-walled circular cross section. This study aims to analyze effect of nonlinear cross-sectional deformation on buckling of CNTs. To accomplish this, CNTs are modeled as beam structures, and the analysis is conducted using the Variational Asymptotic Method (VAM) and a geometrically exact beam theory, as well as nonlinear finite element analysis (FEA). The study considers various loading cases, including pure axial compression and combined loading scenarios, such as bending-axial compression and torsion-axial compression. The results of the study indicate that inclusion of cross-sectional deformation-induced nonlinearity reduces the critical buckling load of CNTs. The reduction is 2–5% for pure axial compression and 10–40% for combined loading cases. The results are validated against existing literature and commercial finite element software, ABAQUS®. Additionally, parametric studies with different slenderness and radius-to-thickness ratios were carried out to further understand the impact of these parameters on buckling of CNTs. Finally, the study presents 3D deformed shapes of CNTs during buckling by combining the results of the 1D analysis and the 2D cross section analysis. The findings show that nonlinearity associated with radius-to-thickness ratio has a significant impact on the cross-sectional ovalisation of CNTs and is critical in evaluating their buckling behavior. This aspect of nonlinearity is often overlooked in continuum modeling methods of CNTs, making this study an important contribution to the field.

LIGHT-TRANSMITTING CONCRETE PROPERTIES OF SHORT WALL PANEL

Consideration of fiber configuration and the distance between the light source or light meter and the LTC specimen in the previous studies is still limited. The incorporation of plastic optical fiber (POF) into concrete with fiber configurations of 5 ´ 5 and 6 ´ 6 grids is investigated in terms of short wall panel application to study its light intensity and strength properties. The light-transmitting concrete (LTC) short wall panel of 300 mm wide ´ 400 mm high ´ 75 mm thick is cast using self-compacting concrete (SCC) to ensure the flowability of the concrete during mixing. The fresh SCC is tested under slump flow, V-funnel, and L-box to verify its fresh properties, while compression test is carried out at 28-days on cube specimens to determine its compressive strength. Then, light transmittance and axial load test under compression are conducted for the LTC wall panel. The findings show that the light intensity of the LTC wall panel increased with the increased number of fiber configurations. However, regardless of fiber configurations, the light intensity reduced with the increase of both light source and light meter distances. In addition, the ultimate axial load of the LTC wall panel with fiber configurations of 5 ´ 5 and 6 ´ 6 grids are 662 kN and 643 kN, respectively. It implies that the fiber configuration does not affect the axial compression load. Furthermore, both LTC wall panels failed solely under pure compression load.

An experiment-based cohesive-frictional constitutive model for cemented materials

Experiment-based damage laws at the contact bond level are often absent in the computational modelling of cemented materials using cohesive contact-bond models. In this paper, in-situ X-Ray Computed Tomography on element-scale cement bonds subjected to pure compression, shear and tensile loading was conducted to investigate their failure mechanisms and associated damage laws. A new cohesive-frictional constitutive model was subsequently developed using results obtained from X-Ray CT tests. The new constitutive model was capable of describing the behaviour of contact bonds subjected to complex loading conditions, including mixed-mode and compression damage. The new model was then implemented in an open-access Discrete Element Code (YADE) to simulate several challenging laboratory-scale tests (e.g., triaxial, Brazilian and Splitting tests) and very good agreements with the experimental data were achieved.

Experimental Investigation on Long-Term Strength and Acoustic Emission Characteristics of Coal Pillar under Inclined Compression Loading

Pillar rheological failure is one of the important reasons to induce earthquake, surface collapse, and water inrush disaster in underground mining engineering. Pillar is generally present under an inclined state and is significantly influenced by combining compression and shear loading. However, many scholars regard the long-term strength of coal or rock mass under pure uniaxial compression loading as the main evolution index of pillar strength, which is not consistent with engineering practice. In this paper, a new inclined uniaxial compression strength (IUCS) test system was developed and then used to carry out the IUCS test and creep test of coal specimens combined with an acoustic emission (AE) technology at various inclination angles (0°, 5°, 10°, 15°, and 20°). The variation of time-dependent deformation, peak strength, long-term strength (LTS), creep fracture model, and AE behavior of the coal with the inclination angels were discussed in detail. The results indicated that the peak strength and LTS of the coal nonlinearly decreased with the inclination angle increasing. The proportion of the peak strength to the LTS had remained constant between 58.5% and 62.9%, which can be considered as the inherent properties of coal rock. The creep failure model of the coal was transformed from tension-splitting failure at the inclination angle of 0° and 5° to tension-shear failure at the inclination angle of 10°-20°, which revealed that the inclination angles were favorable to the initiation and propagation of shear cracks. No matter any inclination angles, AE events can be divided into quiet period, low amplitude rising period, and high amplitude rising period with the periodic mutation of multistage loading points. Moreover, the cumulative AE energy gradually decreases with the increase of the inclination angles, which indicated that the shear stress caused by the specimen inclination can make crack initiation and propagation with less energy absorption. The research results will assist in the long-term strength design and time-dependent stability assessment of the coal pillar.

On the Three-Dimensional Mechanical Behavior of Human Breast Tissue.

As the human breast undergoes complex, large-scale, fully three dimensional deformations in vivo, three-dimensional (3D) characterization of its mechanical behavior is fundamental to its diagnosis, treatment, and surgical modifications. Its anisotropic, heterogeneous fibrous structure results in complex behavior at both the tissue and organ levels. Mathematically modeling of this complex anisotropic behavior is thus critical to the proper simulation of the human breast. Yet, current breast tissue constitutive models do not account for these complexities, so that there is a pressing need for more detailed fully 3D analysis. To this end, we performed a full 3D kinematic mechanical evaluation of human fibroglandular and adipose breast tissues. We utilized our recently developed 3D kinematic numerical-experimental approach to acquire force-displacement data from both breast tissue subtypes. This was done by subjecting cuboidal test specimens, aligned to the anatomical axes,to both pure shear and simple compression loading paths. We then developed novel constitutive model that was able to simulate the unique anisotropic tension/compression behaviors observed. Constitutive model parameters were determined using a detailed finite element model of the experimental setup coupled to nonlinear optimization. We found that human breast tissues displayed complex anisotropic behavior, with strong, directionally dependent non-linearities. This was especially true for the fibroglandular tissue. The novel constitutive model was also able fully capture these behaviors, including states of combined tension and compression (i.e. in pure shear). The results of this study suggest that human breast tissue is complex in its mechanical response, exhibiting varying levels of anisotropy. Future studies will be required to link the observed anisotropy to the physical structure of the tissue, as well as mapping this heterogeneity and anisotropy across individuals.

Experiments on buckling behavior of thin-walled steel pipes subjected to axial compression and external pressure

Pipelines are exposed to various forces in order to develop relative compressive axial and external pressure load in some cases of fluid transmission. An experimental study was conducted to investigate the buckling behavior of thin-walled steel pipes when subjected to a combination of axial compression preloading and external pressure. In addition, the response of some specimens was separately investigated subjected to pure external pressure and axial compression load. A significant reduction was observed in the buckling load and the post-buckling capacity of the thin-walled pipes with increasing the value of axial compression preloading. The existing analytical models for predicting the buckling load of the pipelines were modified. The numerical models were developed and verified using the experimental results, and interaction between the axial load and external pressure was graphically demonstrated for different geometrical ratios.

Sintering graded foamed beads: Compressive properties

AbstractDesigning the foam structures in terms of density and morphology gives the chance to tune their mechanical and functional properties to the specific application. Nowadays, this design has been leveled up by the introduction of graded foams which are characterized by spatially nonuniform densities and/or morphologies. Graded foams have proved superior compared to uniform one in numerous examples and loading conditions but in pure compressive loading, where properties such as the Young's modulus of graded foams are always inferior to uniform ones. When using sintered beads foams, macroscopic pure compression may induce local bending on the single bead, which can be exploited to induce stiffening. This thesis was investigated on both polystyrene and thermoplastic polyurethane samples made by foamed beads sintered in a cylindrical mold. The response to compressive tests of graded foams made by sintering beads having nonuniform cells structures was compared to the uniform counterparts. The results evidenced that, at same average density, foams had up to a 30% ca. of increase of the Young's modulus when the beads are characterized by a denser outer layer.

PARAMETRIC STUDY OF RECTANGULAR REINFORCED CONCRETE COLUMNS CONFINED BY CARBON FIBER REINFORCED POLYMER UNDER AXIAL LOAD

This paper studies the effects of the behavior of normal strength rectangular concrete (NSC) columns confined by carbon fiber-reinforced polymer (CFRP) sheets. Six reinforced concrete columns with dimensions (100mmx100mmx900mm) have been cast and tested. These specimens were subjected to pure axial compressive loading up to failure. Included in the study is the influence of three parameters. Those parameters are the CFRP distribution (5 strips and full wrapping), column slenderness ratio (40, 30), and steel reinforcement ratio (ρ = 0.0113, 0.0314, 0.0678). Those results show a high enhancement in the columns’ load capacity for the first cracking load and the ultimate load for all of the columns.

Experimental Study of Octagonal Steel Columns Filled with Plain and Fiber Concrete under the Influence of Compressive Axial Load with Eccentricity

In recent years, Concrete Filled Tube (CFT) columns have been very much taken into consideration due to the many advantages of the instrument. In experimental studies, the focus has been on compressive loading. Although in many cases the eccentric loading (the presence of a bending moment) has also been investigated, further research is needed in this regard. Therefore, in this study, the steel columns filled with concrete with a regular octagonal cross section were studied under the influence of pressure axial load with eccentricity. The parameters studied in this study include bearing capacity, coefficient of ductility and energy absorption. To test and compare the stated parameters, specimens of 150 cm height, which were filled with plain concrete and fiber reinforced concrete were tested. The compressive axial load has been applied to the specimens by the eccentricity of 50, 100 and 150 mm. The results show that at pure compressive loading, the increase in concrete core capacity increases the load bearing capacity of the specimens so that by increasing the concrete compressive strength by 50%, the bearing capacity of the cross section increases by about 15%. Also, based on the results, the average ductility coefficient for specimens was 7.4, and it seems that this value is independent of the type of loading. The use of concrete with intermediate grade resistance can increase the energy absorbed. However, according to the results, it seems that by increasing the bending moment the positive effects of the concrete core are greatly reduced.

Effects of strain rate variation on the shear adhesion strength of impact ice

In-flight ice accretion on fixed-wing aircraft and rotorcraft can be catastrophic if not mitigated. Most modern ice protection systems are active systems, which require electrical or mechanical power to remove accreted ice, thereby increasing weight, cost, and complexity. Scientists and engineers now seek passive, erosion-resistant materials and coatings with low ice adhesion strength. Ideally, such materials, when applied to vulnerable components of an aircraft, would cause any ice to shed off the surface under normal aerodynamic loading.To aid in the development of low-ice-adhesion-strength materials, the growth and structural behavior of impact ice in a wide range of atmospheric conditions must be characterized. The structural behavior of ice has been examined under pure shear, tension, compression, and mixed-mode loading. However, one important loading consideration that has not been widely investigated on atmospheric ice is strain rate.Knowledge of the relationship between impact ice adhesion strength and strain rate is important because it can be used to design future ice protection systems, and it may dictate the appropriate course of action for a pilot flying through icing conditions—for instance, whether a helicopter pilot should increase the rotor speed rapidly or slowly to induce shedding of the ice.NASA Glenn Research Center funded the design and construction of a new centrifuge-style ice adhesion test rig (“AJ2”) by the Penn State AERTS lab. The ice is accreted dynamically by spinning flat metal test coupons at high speed inside a simulated icing cloud environment. The design and analysis of the AJ2 rig is described in detail in this paper.Experiments were performed using AJ2 to investigate how the adhesion strength of impact ice related to the strain rate applied to it. Stainless steel test coupons of known surface roughness were tested in a range of environmental temperatures. The strain rates applied to the ice ranged between 5E−8 and 5E-5 s−1. It was discovered that a similar power function exists between strain rate and adhesion strength as found in the freezer-ice studies described in the literature. Despite scatter in the data, regression analysis determined the relationship between strain rate, temperature, and adhesion strength to be statistically significant. The power “1/n” for a coupon roughness of 64 nm (Sa) was greater than that of the 80-nm coupon; this was the case for both tested temperatures. However, for the relatively smooth surfaces tested, regression analysis suggested that the surface roughness had negligible effect on adhesion strength. Lower temperatures caused a higher power “1/n” and coefficient “c” in the power function. The variation of the coefficient with temperature is consistent with Glen's power law for the creep of glacier ice in compression. However, Glen did not observe a variation of the power with temperature. The value of “n” in the current study ranged from 2.6 for the smoothest sample at the coldest temperature, to 8.8 for the roughest sample at the warmest temperature. In most cases of the current study, “n” was within the range of previously-reported values in literature (1.5 to 6).

Development and validation of osteoligamentous lumbar spine under complex loading conditions: A step towards patient-specific modeling

Finite-element models are used to investigate the biomechanics of normal, diseased and surgically fused spines. Generally, nominal spine geometries are used to understand the biomechanics, which has created a need for a technique that develops patient-specific lumbar spine geometries. In the current study, a lumbar spine (T12-Sacrum) was developed using a technique that facilitates geometrical morphing, which assists in incorporating patient-specific morphologies into the model. The model evaluations can be used to propose a biomechanically suitable lumbar spine fusion procedure for patients. This study focuses on the validation of the base model under pure-moment, pure-compression and combined-compression-and-moment loadings. Experimental data from the literature were used to validate the response of the model. The L1-L2, L2-L3, L3-L4, L4-L5 and L5-sacrum segments demonstrated a range of motion of 4.5, 4.0, 5.4, 5.0 and 8.9° in flexion; 3.0, 2.5, 3.6, 3.1 and 5.2° in extension; 6.2, 5.8, 6.4, 5.0 and 6.1° in right and left lateral bending; and 2.9, 3.0, 2.9, 1.9 and 2.5° in right and left axial rotation, all under 10 Nm pure-moment loading. The L1-L2, L2-L3, L3-L4, L4-L5 and L5-sacrum discs demonstrated compressions of 1.1, 1.4, 1.6, 1.4 and 0.9 mm under 1200 N follower- or pure-compression loading. With the combined loading of 280 N follower and 7.5 Nm moment, the L1-L5 model demonstrated 11.7, 7.2, 18.3 and 10.4 degrees of range of motion in flexion, extension, bending and rotation, respectively. The model results were in good agreement with corridors from six different experimental studies and can be used for future clinical studies.

Assessment of axial load carrying capacity of GFRP funicular shells with steel mesh

This paper presents the test results of an experimental program to investigate the load-bearing capacity of twenty-seven Glass Fibre Reinforced Polymer GFRP funicular shells under pure compression load. The test parameters include the number of glass fiber layers, the rise of shells and the effect of inclusion of steel mesh as an additional reinforcement to the glass fiber. Comparisons between the experimental test results of various parameters are performed in terms of the ultimate load-carrying capacity. A parametric study was conducted which showed the significant effect of the increasing rise on the load bearing capacity of GFRP shells. In general, the results of this study revealed that the ultimate load-carrying capacity gets increased by nearly 58% by increasing the number of normal glass fiber layers from two to four. Moreover, an increase in the ultimate load-carrying capacity of nearly 15% to 26% was observed with the inclusion of steel mesh as an additional reinforcement to the glass fiber. In the latter case, the deflections were comparatively lesser than the former. The failure loads of all the specimens were found and two equations were proposed to express the relation between rise, span to rise ratio, with ultimate load. It is concluded that the ultimate loads are a function of the rise of the shell and the number of fiber layers. The addition of steel mesh increases stiffness of shells, there by reduces total deflection.

Influence of concrete humidity on the temperature development under fatigue compressive loading

Due to research activities on the topic of concrete mixtures during the last decades concrete compressive strength could be increased significantly. At the same time the lifespan of concrete structures has been continuously extended. Therefore, the fatigue behavior of modern High Performance Concrete (HPC) becomes more important with respect to service life. Previous studies on normal strength concrete have shown that the number of cycles to failure under pure compressive cyclic loading mainly depends on frequency and amplitude. An increase of the loading frequency leads to a higher number of load cycles to failure. Recent research work shows that the humidity of the specimen is also influencing the fatigue behavior of concrete. Conditioning of the test specimen to high humidity led to significant lower fatigue life. Other research activities on high strength concrete point out the effect of the loading frequency on load induced heat effects of the concrete. The experimental study presented here aims on the influence of the humidity on the temperature development under fatigue compressive loading and on the number of cycles to failure. It comprises three fatigue test series at a test frequency of 10 Hz with sealed cylindrical specimens of the same concrete with different degrees of humidity. In addition, destructive and non-destructive tests were carried out on damaged and undamaged concrete.