Increase In Load-bearing Capacity Research Articles

Shear retrofitting of reinforced concrete beams with steel fiber reinforced concrete

With the objective of evaluating the performance of steel fiber reinforced concrete (SFRC) as a retrofitting material for reinforced concrete beams the experimental study of reinforced concrete beams repaired and strengthened with a SFRC jacketing and tested under shear is presented in this paper.The reinforced concrete beams were designed with high amount of longitudinal steel and minimum transverse reinforcement so that they present shear failure. Some of the beams were strengthened with very fluid high strength SFRC jacketing and some of them were first tested under shear to produce some damage and then they were repaired with the same technique. Plain concrete and SFRC with two different fiber dosages, 30kg/m3 and 60kg/m3, were used for the reinforcement.The experimental program showed the possibility of performing the retrofitting at work place. The repaired beams showed excellent strength and deformation capacity restitution. The strengthened beams exhibited increase of load bearing capacity. The addition of fibers to the concrete played an important role in the prevention of the jacketing debonding from the beams.

Increase of load bearing capacity of a square-form nanofilter

Square-form, multi-layered nanofilter membranes have been investigated experimentally and by numerical simulation to determine their load bearing capacity versus filtration ability. The effect of various topologies combining the thickness of a load-carrying layer and Si-reinforcement on the bursting pressure has been determined. Based upon the comparison of a performance index an optimal structure could be selected for later production.

Development of advanced duplex surface systems by combining CrAlN multilayer coatings with plasma nitrided steel substrates

Both modelling analyses and experimental work have recently confirmed that the failure of thin coatings on steel, especially under high loads for some demanding applications, is related to the lack of mechanical support from the substrate, which means that the exceptional hardness, toughness and wear resistance of state of the art PVD coatings cannot be fully exploited. To this end, two types of new duplex surface systems have been developed from this research: i) PVD (specifically Closed Field UnBalanced Magnetron Sputter Ion Plating, CFUBMSIP) CrAlN multilayer coating deposited on ex-situ, 20-h active-screen plasma nitrided (ASPN) steel samples, and ii) in-situ 3-h, high power medium frequency pulsed plasma nitriding (HPMFPPN) treatment, followed by a similar CrAlN coating, but performed in a serial, single batch process in an otherwise conventional CFUBMSIP equipment. The microstructures of these two duplex surface engineered systems were characterised using XRD and SEM, while their hardness, adhesion, load bearing capacity and tribological properties were compared by micro-hardness tests, scratch adhesion tests and pin-on-disc sliding wear measurements. Post-test examinations were conducted and the results confirmed that a hard coating on a nitrided substrate can fully exploit the advantages of both the nitrided sub-surfaces for increased load bearing capacity and of the PVD coating for increased hardness, high temperature stability and extreme wear resistance. Finally, the advantages and disadvantages of these two new duplex surface systems were compared and their potential applications were discussed.

Fire behavior of eccentrically loaded slender high strength concrete-filled tubular columns

This paper describes a series of 24 fire tests conducted on slender circular hollow section columns filled with normal and high strength concrete, subjected to eccentric axial load. It is a continuation of a previous research paper (Romero et al., 2011 [1]), where test results on centrally loaded columns were presented. The test parameters covered in this fire testing program were the nominal strength of concrete (30 and 90MPa), the infilling type (plain, bar-reinforced and steel fiber reinforced concrete), the axial load level (20% and 40%) and the load eccentricity (20 and 50mm). The columns were tested under fixed-pinned boundary conditions, with a relative slenderness at room temperature higher than 0.5 for all the specimens. The aim of this paper is to study the influence of eccentricity in combination with the type of concrete infill. The results show that the addition of steel fibers does not improve the fire resistance of slender columns under eccentric loads, as compared to columns filled with plain concrete. However, the addition of reinforcing bars increases the fire resistance of the columns in this situation. Filling the steel hollow section columns with concrete increases their fire resistance, the increase in load bearing capacity being more noticeable for columns filled with high strength concrete. A comparison with the current simple calculation model in Eurocode 4 Part 1.2 shows that, although the method is safe for eccentrically loaded columns, it produces a high error in the predictions for columns filled with plain or steel fiber reinforced concrete.

Study on Strengthening Glued-Laminated Timber with Aramid Cords and Properties of Composite Materials

This paper presents method of strengthening glued-laminated timber with aramid cords. In order to estimate the increase in load-bearing capacity, numerical analysis was carried out on three beams: unreinforced; reinforced with one layer of aramid cords; and reinforced with two layers of aramid cords. A preliminary numerical analysis showed a reduction of deflections of reinforced beams by about 11 to 14 % and a reduction of 19 to 25 % of normal stress.

Load-Bearing Capacity of the Footing Resting on a Reinforced Fly Ash Slope

In several parts of the world, disposal of waste materials such as fly ash is a great problem. Application of waste materials as structural fills in foundations is one of the best solutions to disposal problems, because wastes can be used in large volumes in such applications. There may be difficulty due to poor load-bearing capacity of fly ash, especially when footing rests on the top of the fly ash fill slope. Inclusion of polymeric reinforcements as horizontal sheets within the fill may be one of the most viable solutions to improving the load-bearing capacity of reinforced fly ash slope, and it is particularly important for the situations where foundations need to be located either on the top of a slope or on slope itself. The present work is aimed at investigating the efficacy of a single layer of reinforcement in improving the load-bearing capacity when it gets incorporated within the body of a model fly ash embankment slope. An increase in load bearing capacity due to the incorporation of reinforcement in the model slope was found by conducting laboratory tests. Experimental results were compared by numerical values obtained using software GEO5 and PLAXIS.

EcoForge: Resource-Efficient Process Chains for High Performance Parts

Classical forging process chains for the production of high performance parts consist of heating, hot forming, machining and heat treatment stages. Especially the last stage comprises numerous energy consumptive heating and cooling procedures. Consolidation of these process chains has a large energy-saving potential and thus can lead to ecological and economic advantages. In addition, the optimization may result in well enhanced local material properties in the final part. Therefore, the collaborative research project “EcoForge: Resource-efficient process chains for high performance parts” has been initiated. Five renowned research institutes aim at optimising the industrially relevant process chain in order to facilitate the resource-efficient production of forgings with increased load bearing capacity. The six subprojects of EcoForge include both, numerical investigations on the microstructure evolution and cooling behaviour of the forged parts as well as numerous experiments which will be carried out in collaboration with the project’s industrial consulting committee, summarising up to 50 relevant participating companies. The joint project is funded by the AiF and BMWi aiming at major areas of technical developments in Germany.

The effectiveness of CFRP materials strengthening of eccentrically compressed reinforced concrete columns

In the paper the investigations of load-bearing capacity of eccentrically compressed reinforced concrete columns strengthened with CFRP strips and sheets are presented. The aim of the conducted researches was to estimate the influence of changeable longitudinal CFRP reinforcement intensity on load-bearing capacity of columns. In the experimental investigations three longitudinal CFRP strengthening intensities were applied – 2.10%, 1.68% and 1.26%. The experimental tests were performed on columns models with cross-section of 200×200 mm and height of 1 500 mm. The investigative members were loaded axially or eccentrically. The eccentric force was exerted in the area of cross-section core (h/12 and h/6 from neutral axis). In the paper the results of experimental studies on load-bearing capacity depending on longitudinal strengthening intensity were presented and discussed. The failure mechanisms were described. The values of failure force and maximum longitudinal strain were given. The application of longitudinal CFRP strips (as external composite strengthening) causes the increase of column rigidity. Additional transverse strengthening implies delay in debonding the strips from concrete. The interaction of both CFRP materials entails the reduction of strains increase velocity which transfers to the increase of load-bearing capacity.

RESEARCH ON LOAD CAPACITY OF CONCRETE FILLED COLUMNS WITH BATTENED STEEL SECTIONS

The paper presents experimental and numerical results for selected built‐up steel columns filled with concrete. The laboratory tests were accompanied by numerical analysis carried out using general purpose, finite element program ABAQUS. Based on heretofore research presented in this paper, one may assumes that the application of concrete filled columns with battened steel sections is economically very profitable. For columns filled with concrete strength class C20/25 the increase of load bearing capacity was 42% and for elements filled with concrete strength class C50/60 ‐ above 100%. The application of the shorter distance between battens allowed to obtain additional increase of ultimate load (for concrete C20/25 ‐ about 8%). The numerical analysis also confirmed the increase of the load capacity for the columns. The best correlation between numerical and experimental results was obtained for the assumed eccentricity of 1 mm. Moreover the higher rigidity of those members in relation to steel columns is not connected with significant increase of the cost. The study was conducted as a part of the research project nr 4TO7E01528, founded by the Polish Ministry of Science and Higher Education. Santrauka Straipsnyje pristatomi plieniniu kolonu, užpildytu dvieju tipu betonu, eksperimentiniai ir skaitiniai tyrimu rezultatai. La‐boratoriniai bandymai ir skaitine analize buvo atliekami naudojant bendrosios paskirties baigtiniu elementu programa ABAQUS. Remiantis šiame straipsnyje pateiktais tyrimo rezultatais, galima daryti prielaida, kad kolonos iš standžiu plieniniu skerspjūviu, užpildytu betonu, yra labai ekonomiškos. Kolonos, užpildytos C20/25 betonu, laikomoji galia padidejo 42 %, o elemento, užpildyto C50/60, ‐ daugiau negu 100 %. Kai atstumas tarp sutvirtintu vietu trumpesnis, galima padidinti didžiausiaja apkrova (naudojant betono klase C20/25 ‐ apie 8 %). Skaitine analize patvirtino padidejusia kolonu laikomaja galia. Geriausia koreliacija tarp eksperimentiniu ir skaitiniu rezultatu buvo gauta esant tariamam 1 mm ekscentricitetui. Be to, didesnis šiu elementu standumas, palyginti su plieninemis kolonomis, nera susijes su išlaidu padidejimu. Šis mokslinis tyrimas buvo mokslinio projekto Nr. 4TO7E01528, kuri inicijavo Lenkijos studiju ir aukštojo mokslo ministerija, dalis.

Experimental Study of the Advanced Transient Concrete Model on Reinforced Concrete Columns During Fire Exposure

The advanced transient concrete model (ATCM) is an extended model for concrete in compression at elevated temperature that incorporates elastic, plastic and creep strain as a function of temperature and stress history. The ATCM is applied with the material model of the thermal induced strain model. The non-linear model comprises thermal strain, elas- tic strain, plastic strain and transient temperature strains and load history modelling of restraint concrete structures sub- jected to fire. The mechanical strain calculated as a function of elastic strain, plastic strain and thermal induced strain. The thermal induced strain is relative independent compared to dependence of Young's Modulus by load history. Actually the term comprises elastic, plastic and (pure) transient creep strains as we will show. A comparison is given between experi- mental results with cylindrical specimens and calculated results. The equations of the ATCM consider a lot of capabilities, especially for considering irreversible effects of temperature on some material properties. By considering the load history during heating up, an increasing load bearing capacity due to a higher stiffness of concrete may be obtained. With this model it is possible to apply the thermal-physical behaviour of ma- terial laws for calculation of structures under extreme temperature conditions. The effect of load history in highly loaded structures under fire load will be investigated. The theoretical basis is given in this supplement added with an experimental study of concrete columns with various mixes.

An Advanced Transient Concrete Model for the Determination of Restraint in Concrete Structures Subjected to Fire

The advanced transient concrete model (ATCM) is an extended model for concrete in compression at elevated temperature that incorporates elastic, plastic and creep strain as a function of temperature and stress history. The ATCM is applied with the material model of the thermal induced strain model. The non-linear model comprises thermal strain, elastic strain, plastic strain and transient temperature strains and load history modelling of restraint concrete structures subjected to fire. The mechanical strain is calculated as a function of elastic strain, plastic strain and thermal induced strain. The thermal induced strain is relative independent compared to dependence of Young's modulus by load history. Actually the term comprises elastic, plastic and (pure) transient creep strains as we will show. A comparison is given between experimental results with cylindrical specimens and calculated results.The equations of the ATCM consider a lot of capabilities, especially for considering the irreversible effects of temperature on some material properties. By considering the load history during heating up, an increasing load bearing capacity due to a higher stiffness of concrete may be obtained. With this model it is possible to apply the thermal-physical behaviour of material laws for calculation of structures under extreme temperature conditions. The effect of load history in highly loaded structures under fire load will be investigated. The theoretical basis is given in this paper.

Effects of Selective Androgen Receptor Modulator (SARM) Treatment in Osteopenic Female Rats

Although androgens are known to protect bone, side effects and poor oral bioavailability have limited their use. We previously reported that S-3-(4-acetylamino-phenoxy)-2-hydroxy-2-methyl-N-(4-nitro-3-trifluoromethyl-phenyl)-propionamide (S-4) is a potent and tissue-selective androgen receptor modulator (SARM). This study was designed to evaluate the skeletal effects of S-4 in an osteopenic model. Aged female rats were gonadectomized or sham operated on day 1 and assigned to treatment groups. Dosing was initiated on day 90 and continued daily until day 210. Whole animal bone mineral density (BMD), body weight, and fat mass were determined by dual energy x-ray absorptiometry (DEXA). Regional analysis of excised bones was performed using DEXA or computed tomography. Femur strength was evaluated by 3-point bending. S-4 restored whole body and lumbar vertebrae (L5-L6) BMD to the level of intact controls. Significant increases in cortical bone quality were observed at the femoral midshaft, resulting in increased load bearing capacity. S-4 demonstrated partial/complete recovery of bone parameters to age-matched intact levels. Increased efficacy observed in cortical bone sites is consistent with reported androgen action in bone. The ability of S-4 to promote bone anabolism, prevent bone resorption, and increase skeletal muscle mass/strength positions these drugs as promising new alternatives for the treatment of osteoporosis.

Load-bearing capacity of plain concrete walls

Walls in housing are usually made of masonry or reinforced concrete. These wall constructions are both labour- and material-intensive and therefore more expensive than walls made of plain concrete. The high wall-thickness required by the design rules of BS 8110-1 and Eurocode 2 is the most important restraint for the use of plain concrete walls. The different design approaches are discussed and a new design method is explained in this paper. The proposed model allows for a simple, standardised and economic design of plain concrete walls with a thickness less than that of masonry walls. A further increase in load-bearing capacity can be achieved by taking into account the concrete tensile strength. A comparison with a test database verifies that all relevant aspects of the load-bearing capacity, for example slenderness, eccentricity and concrete strength, are represented appropriately by the developed design method. Moreover, the safety level of EN 1990 can be achieved.

Calculation of a Tunnel Cross Section Subjected to Fire – with a New Advanced Transient Concrete Model for Reinforced Structures

The paper presents the structural application of a new thermal induced strain model for concrete – the TIS-Model. An advanced transient concrete model (ATCM) is applied with the material model of the TIS-Model. The non-linear model comprises thermal strain, elastic strain, plastic strain and transient temperature strains, and load history modelling of restraint concrete structures subjected to fire.The calculations by finite element analysis (FEA) were done using the SAFIR structural code. The FEA software was basically new with respect to the material modelling derived to use the new TIS-Model (as a transient model considers thermal induced strain). The equations of the ATCM consider a lot of capabilities, especially for considering irreversible effects of temperature on some material properties. By considering the load history during heating up, increasing load bearing capacity may be obtained due to higher stiffness of the concrete. With this model, it is possible to apply the thermal-physical behaviour of material laws for calculation of structures under extreme temperature conditions.A tunnel cross section designed and built by the cut and cover method is calculated with a tunnel fire curve. The results are compared with the results of a calculation with the model of the Eurocode 2 (EC2-Model). The effect of load history in highly loaded structures under fire load will be investigated.A comparison of this model with the ordinary calculation system of Eurocode 2 (EC2) shows that a better evaluation of the safety level was achieved with the new model. This opens a space for optimizing concrete structure design with transient temperature conditions up to 1000 °C.

COMPOSITE AND INTERACTION EFFECTS IN STEEL‐CONCRETE STRUCTURES FOR HIGHER FIRE RESISTANCE

Wide application of steel structures for office and industrial buildings is one of the main features of Lithuanian and world building industry. This fact is related to an essentially wider use of new structural solutions, new structural members and materials. Usage of different types of materials in one structural system for better utilisation of positive properties of each component is very popular in current building industry. Composite beams, columns, beams‐columns and composite floors can be mentioned. Structures that were designed and erected twenty or more years ago are mostly a collection of different types of structural elements. In general, interaction or composite effect is not taken into account, when designing such structures. Though a considerable number of roofs and ceilings made up of reinforced concrete slabs and steel beams or steel trusses are still in maintenance. Structural solution of the slabs, welding of embedded steel parts of slabs to steel structures, filling with concrete the joints between slabs create the conditions for interaction of slabs and steel structures. The result of this effect is that slabs take up a part of the internal forces of the steel structures and consequently diminish it in steel beams and trusses. It is obvious that this fact leads to the increase of load bearing capacity and fire resistance. The paper deals with the problem of evaluation of composite and structures interaction effect on fire resistance.

Experimental and analytical technique for estimating interface thermal conductance in composite structural elements under simulated fire conditions

Composite structural elements in the form of steel tubes filled with concrete are being increasingly used in buildings for their dual advantage of increased load bearing capacity and fire resistance. Models to predict the response of composite structures under fire conditions have been developed with varying degrees of accuracy. One of the major drawbacks for these models is ignoring the effect of thermal contact resistance at the steel–concrete interfacial. The reason for this oversight is due mainly to the absence of data in the literature quantifying this parameter. This paper summarizes an experimental and analytical investigation of the interfacial thermal contact conductance of an unloaded circular steel tube filled with non-reinforced normal concrete and exposed to high heat fluxes. Inverse heat conduction analysis and experimental measurements are used to estimate the thermal contact conductance as a function of steel temperature. Sensitivity analysis of the effect of the magnitude of the contact conductance on the temperature response of the composite element using direct heat conduction modelling is also presented.

Evaluation of duplex coatings produced with a pulsed Nd:YAG laser and filtered arc

Duplex coatings combining a physical vapour deposition (PVD) thin film and laser-clad WC/Ni layer were produced on an austenitic steel substrate. PVD TiN, TiCN and TiC thin films were deposited using a filtered arc deposition system. Laser-clad WC/Ni layers were produced using a pulsed Nd:YAG laser and optical fibres. Mechanical properties (microhardness and adhesion) of the coatings were determined using a Ultra-Micro Indentation System (UMIS-2000) and adhesion scratch tester, respectively. The wear resistance of the duplex coatings was evaluated by a pin-on-disc wear tester. The results showed that increasing the concentration of carbon in the PVD thin films increases its hardness, reduces its adhesion to the clad layer and increases its wear resistance. All coatings withstood the applied loads (25 and 40 N) and no sign of breakthrough was observed on any of them. This indicated that the duplex coatings exhibited a significant increase in load-bearing capacity, confirming the pivotal role of the laser-clad layer in supporting the applied load.

Lateral stability of coupled simply supported beams

The lateral stability of beams is analysed with concentrated force acting on the upper flange. The disadvantageous effect of this load position is not so severe when the load is taken by two parallel beams that are connected by an element. This is the case of the crane girders at which the gantry yields such a connection. Here the less heavy beam affords a lateral restraint that results in the increase of the critical force. After deriving the equilibrium equations a parametric study was carried out on simply supported beams. The results of this study were approximated by easy to handle formulas for the critical force. Using these formulae practical application was also shown. According to a relevant design code the resistance of the more heavily loaded beam was calculated. Compared to the resistance of a stand-alone beam the increase in load bearing capacity due to the interaction was pointed out.

INVESTIGATIONS IN THE STRENGTH OF PRESTRESSED MULTILAYERED BEAMS UNDER THE ACTION OF LONG-TERM SHEAR/MEDINIŲ IŠ ANKSTO ĮTEMPTŲJŲ DAUGIASLUOKSNIŲ SIJŲ STIPRUMAS VEIKIANT ILGALAIKĖMS SKERSINĖMS JĖGOMS

The results of long-term experiments are presented in the paper. As a result of the experiments, invention SU 1025831 was developed under the name “The method of manufacture of a timber load-bearing element” (E 04 C 3/12, priority since July 11, 1981). The objective of the experiments performed was to check the method of increase of load bearing capacity of glulam beams under the influence of long-term shear. 14 beams were tested: nine of them were multilayered and 5 made of board-package and square-sawn timber. All the beams failed because of the action of shear forces. Two beams were tested by static short loading, the rest twelve by long-term loading. Three beams, that have not failed because of the action of long-term loading, then were tested by short-term loading. From the tests of multilayered, glulam and solid square-sawn timber beams the decrease of the relative strength wood split alongside fibres under the action of long-term shear is bigger than that given in literature in case of standard experiments. Relationship of the level of decrease of this strength with the duration of long-term loading may be calculated according to the equation (2). The influence of long-term loading on the load-bearing capacity of these beams depends on the intensity of actions: if such a load does not cause the plastic deformations in the beam, their load-bearing capacity does not decrease and vice versa—the appearance of plastic deformations and micro-cracks means the decrease of load bearing capacity of the beam under a short-term shear. A short description of invention SU 1025831 is also presented in the paper. The invention is devoted to the perfection of the former invention No 954237. The latter one suggested an increase of load-bearing capacity of glulam elements under a short-term shear. Under a long-term load, or in case of fire, when the temperature and moisture around is changing, the strength of prestressed joint of these beams may not be fully guaranteed because of the influence of inner stresses and possible micro-cracking. With the purpose to increase the strength of beams under a long-term shear the author offers additionally to install pivots (Fig 6, 3) after giving prestress and full polymerisation. This method does not only increase the load-bearing capacity of multilayered elements under a long-term shear, but also ensures a higher reliability and fire resistance of such structures.

INVESTIGATIONS IN THE STRENGTH OF GLULAM MULTILAYERED BEAMS UNDER A SHORT-TIME SHEAR/MEDINIŲ KLIJUOTŲ DAUGIASLUOKSNIŲ SIJŲ STIPRUMO TYRIMAI VEIKIANT TRUMPALAIKĖMS SKERSINĖMS SKERSINĖMS JĖGOMS

The author of the article has performed wide-range tests of glulam beams. The objective of the tests is increasing of load bearing capacity of such beams under shear. As a result 5 inventions have been suggested and confirmed. In total 44 beams of various types were tested under the action of short and long-time loadings. These investigations have verified a new method for increasing load bearing capacity of glulam beams. The essence of the method was the utilisation of prestressed elements in multilayered beams. It allows to increase load bearing capacity of such elements under shear and decrease or eliminate the influence of lateral tension stresses on their resistance. Totally, 30 beams have been tested for the influence of short-time forces: 6 of them are multilayered with pre-stressed elements, made by the offer of invention No 954237; 8 analogous beams for comparison of the results are made of squared timber, board package, multilayered without prestressed elements; 16 different beams for additional investigations of methods of experiments and closer definition of separate technological factors. All beams failed because of shear. It has been proved by experiments that plywood brass in multilayered beams not only increases the strength of the beam, but also prevents the element from a sudden failure, increases its reliability. Longitudinal cracks have appeared in the zones of neutral axes of prestressed multilayered beams before the failure of them, while the load was 0,93–0,98 of ultimate the width of the crack was 0,7–0,8 mm, and the shear deformation was 2–6 mm at the moment of failure. The strength of the beams under short-time shear depending on the level of prestressing force (σy = = 1,5…2,25 MPa) increased 9–10% and crack resistance increased 9–22% in comparison with unpresstressed beams. A short description of invention No 954237 has also been given (see Fig 6). Layers of a load bearing multilayered element with wood fibres oriented along the axis of the member (1) are precompressed laterally to the wood fibres (5). Compression force should not cause stresses (σy) higher than the point of wood proportionality in lateral direction. These layers (1) are glued with the layers where wood fibres are directed laterally to the axis of the element (2) and they are shorter in value Δ ≥ σy · h/E90 than layers (1). Horizontal prestressing of multilayered element (4) has to ensure a qualitative cohesion. It is possible to use structural plywood instead of wood layers with fibres lateral to the axis of the element. The use of this method does not only increase the resistance of glulam elements to short-time shear, but also ensures a better reliability of such structures.