Neoprene Pads Research Articles

Investigation of the influence of different surface regularization methods for cylindrical concrete specimens in axial compression tests

ABSTRACT This study was conducted with the aim of evaluating the influence of different methods for end surface preparation of compressive strength test specimens. Four different methods were compared: a mechanical wear method through grinding using a diamond wheel established by NBR 5738; a mechanical wear method using a diamond saw which is established by NM 77; an unbonded system using neoprene pads in metal retainer rings established by C1231 and a bonded capping method with sulfur mortar established by NBR 5738 and by NM 77. To develop this research, 4 concrete mixes were determined with different strength levels, 2 of group 1 and 2 of group 2 strength levels established by NBR 8953. Group 1 consists of classes C20 to C50, 5 in 5MPa, also known as normal strength concrete. Group 2 is comprised of class C55, C60 to C100, 10 in 10 MPa, also known as high strength concrete. Compression tests were carried out at 7 and 28 days for the 4 surface preparation methods. The results of this study indicate that the method established by NBR 5738 is the most effective among the 4 strengths considered, once it presents lower dispersion of values obtained from the tests, measured by the coefficient of variation and, in almost all cases, it demonstrates the highest mean of rupture test. The method described by NBR 5738 achieved the expected strength level in all tests.

A Novel Cooling Method and Comparison of Active Rewarming of Mildly Hypothermic Subjects

To compare the effectiveness of arteriovenous anastomosis (AVA) vs heated intravenous fluid (IVF) rewarming in hypothermic subjects. Additionally, we sought to develop a novel method of hypothermia induction. Eight subjects underwent 3 cooling trials each to a core temperature of 34.8±0.6(32.7 to 36.3°C [mean±SD with range]) by 14°C water immersion for 30 minutes, followed by walking on a treadmill for 5 minutes. Core temperatures (Δtes) and rates of cooling (°C/h) were measured. Participants were then rewarmed by 1) control: shivering only in a sleeping bag; 2) IVF: shivering in sleeping bag and infusion of 2 L normal saline warmed to 42°C at 77 mL/min; and 3) AVA: shivering in sleeping bag and circulation of 45°C warmed fluid through neoprene pads affixed to the palms and soles of the feet. Cold water immersion resulted in a decrease of 0.5±0.5°C Δtes and 1±0.3°C with exercise (P < .01); with an immersion cooling rate of 0.9±0.8°C/h vs 12.6±3.2°C/h with exercise (P < .001). Temperature nadir reached 35.0±0.5°C. There were no significant differences in rewarming rates between the 3 conditions (shivering: 1.3±0.7°C/h, R2 = 0.683; IVF 1.3±0.7°C/h, R2 = 0.863; and AVA 1.4±0.6°C/h, R2 = 0.853; P = .58). Shivering inhibition was greater with AVA but was not significantly different (P = .07). This study developed a novel and efficient model of hypothermia induction through exercise-induced convective afterdrop. Although there was not a clear benefit in either of the 2 active rewarming methods, AVA rewarming showed a nonsignificant trend toward greater shivering inhibition, which may be optimized by an improved interface.

Existing prefab R/C industrial buildings: Seismic assessment and supplemental damping-based retrofit

A research study on prefab reinforced concrete buildings designed with older Technical Standards is presented in this paper, where attention is focused on hall-type industrial structures. A representative case study, which includes the main sources of seismic vulnerability, is examined in detail. The possible rigid rotation of the bottom end zone of columns, which are encased in smooth socket-type foundations, and the frictional contact between the neoprene pads situated on top of the columns and the terminal zone of the roof girders are modelled in time-history assessment analyses. Initially carried out by assuming an elastic behaviour of columns, the analyses highlight unsafe response conditions under seismic action scaled at the basic design earthquake level, and near-collapse caused by the loss of support of several girders from the neoprene pads at the maximum considered earthquake level. A second step of the analyses, where plastic behaviour of columns is investigated by incorporating fiber-type plastic hinges at their bottom end sections, shows a remarkable ductility demand, as well as potential collapse induced by the complete loss of support of girders. The high lateral displacements of columns may also cause failure of the fastenings of the connected cladding panels, likely to result in their overturning-induced collapse. Based on these data, a supplemental damping-based retrofit hypothesis is suggested, consisting in the installation of dissipative braces equipped with pressurized fluid viscous spring-dampers. The protective system allows attaining a completely undamaged response of structural and non-structural members, and therefore meeting the requirements of the Immediate Occupancy limit state, up to the maximum considered earthquake level.

Real‐time damage detection based on pattern recognition

AbstractStructural health monitoring (SHM) can be defined as the process of developing and implementing structural damage detection strategies. Ideally, this detection should be carried out in real time before damage reaches a critical state and impairs structural performance and safety. Hence, it must be based on sensorial systems permanently installed on the target structures and on fully automatic detection methodologies.The ability to detect damage in real‐time is vital for controlling the safety of old structures or for post‐retrofitting/post‐accident situations, where it might even be mandatory for ensuring a safe service. Under these constraints, SHM systems and strategies must be capable of conducting baseline‐free damage identification, i.e. they must not rely on comparing newly acquired data with baseline references in which structures must be assumed as undamaged.The present paper describes an original strategy for baseline‐free damage detection based on the application of artificial neural networks and clustering methods in a moving windows process. The proposed strategy was tested on and validated with numerical and experimental data obtained from a concrete cable stayed bridge and proved effective for the automatic detection of small stiffness reductions in single stay cables as well as the detachment of neoprene pads in anchoring devices, requiring only a small number of inexpensive sensors.

On-line unsupervised detection of early damage

Structural health monitoring (SHM) strategies should ideally consist of continuous on-line damage detection processes, which do not need to rely on the comparison of newly acquired data with baseline references, previously defined assuming that structural systems are undamaged and unchanged during a given period of time. The present paper addresses the topic of SHM and describes an original strategy for detecting damage in an early stage without relying on the definition of data references. This strategy resorts to the combination of two statistical learning methods. Neural networks were used to estimate the structural response, and clustering methods were adopted for automatically classifying the neural networks' estimation errors. To ensure an on-line continuous process, these methods were sequentially applied in a moving windows process. The proposed original strategy was tested and validated on numerical and experimental data obtained from a cable-stayed bridge. It proved highly robust to false detections and sensitive to early damage by detecting small stiffness reductions in single stay cables as well as the detachment of neoprene pads in anchoring devices, resorting only to a small amount of inexpensive sensors. Copyright © 2015 John Wiley & Sons, Ltd.

Experimental investigation of the cyclic response of reinforced precast concrete framed structures

This paper summarizes the results of an experimen- tal program devoted to assessing the main structural characteristics and criticalities in the seismic response of typical reinforced precast concrete structures in Italy that were severely damaged by major earthquakes in May 2012. Two 3⁄4 scale two-bay, three-story precast concrete frames with and without cladding panels were subjected to a quasi-static cyclic top displacement his- tory consisting of symmetric stepwise increasing drift cycles. Pinned beam-column connections consisted of neoprene pads with vertical steel dowels working in shear. The flexibility of the cantilevered static scheme forced large displacement demand and incompatible transfer of the horizontal forces to occur in joints lack- ing shear and ductility capacity. In addition, displace- ment incompatibility between structural elements and cladding panels caused the premature failure of their connections. The results demonstrate the inadequate performance of this structural solution because of its beam-to-column and panel-to-structure connection systems, the responses of which reaffirm that this frame typology should not be used in areas of high seismic hazard because of its nearly elastic-fragile behavior.

Seismic Performance of Precast Industrial Facilities Following Major Earthquakes in the Italian Territory

Recent major earthquakes in the Italian territory have reaffirmed the seismic vulnerability of precast industrial buildings typical of past Italian building practices, highlighting structural deficiencies observed during previous events and primarily related to the transfer of horizontal forces between structural and nonstructural elements. An intrinsic lack of shear and ductility capacity has been observed in simply supported beam-to-joist and beam-to-column connections, primarily constituted by vertical steel dowels or solely relying on shear friction, with or without neoprene pads. These connections were designed neglecting seismic loads and their premature failure was observed during recent seismic events to cause a loss of support of beam elements, owing to the relative movements of elements, and the collapse of part of the buildings, primarily the roof. The seismic displacement demand of the industrial buildings under consideration is larger than traditional RC frame structures owing to their higher flexibility, according to both higher interstory height and to a cantilevered static scheme. Furthermore, this high flexibility may also result in displacement incompatibility between structural and nonstructural elements, such as precast cladding panels, causing their connection failure. On the basis of detailed field observations on a relevant number of buildings, collected just after the earthquakes, seven representative industrial facilities are examined to outline the primary vulnerabilities of one-story precast concrete structures not designed and detailed for seismic loads.

Structural GFRP Permanent Forms with T-Shape Ribs for Bridge Decks Supported by Precast Concrete Girders

A new concrete bridge deck cast onto glass fiber–reinforced polymer (GFRP) stay-in-place (SIP) structural forms is studied. The forms, which replace the bottom layer of conventional rebar, are essentially flat plates with T-up ribs. They span between support girders spaced at 1,772 mm and are lap-spliced using adhesive and mechanical fasteners. Special attention was given to the detailing of monolithic connections between the deck and girders to simulate continuity. The flange of the supporting concrete girders had a rough surface finish and protruded steel stirrups and mimicked AASHTO Type III girders. Five full-scale decks were tested to (1) compare the novel system with a conventional RC deck, (2) examine the effect of eliminating a top layer of orthogonal GFRP rebar, (3) assess a practice commonly used in bridge deck tests of using simple spans resting on neoprene pads, neglecting connection to girders, and (4) examine a commercially available all-GFRP deck, using the same GFRP panels but with a top GFRP plate fastened to the T-up ribs. Four auxiliary flexural specimens were tested to examine the lap-splice. The concrete deck with GFRP SIP form showed 33% higher strength than the conventional RC deck. It also achieved a peak load 7.8 times higher than the service load plus impact. Deflection under the service load was less than span/1,600. Remarkable deformability and pseudoductility was achieved at ultimate load, beyond punching shear, because of the progressive failure of the lap-splice. The simply supported deck failed at a slightly lower strength than the monolithically cast one but had a much lower stiffness.

Capping Systems for High-Strength Concrete

This study focused on the effects of capping systems on the compressive strength of high-strength concrete (HSC). The three systems investigated were ground ends, bonded caps, and unbonded pads. Five compressive strength groups were examined with strength levels ranging from 6,000 psi to 14,000 psi. The capping compounds investigated were commercially available and advertised for testing HSC. The unbonded pads were neoprene pads with a Shore A Durometer hardness of 70. A grinding machine was used to obtain the required planeness and perpendicularity on the ground end cylinders. No significant difference was found between the capping systems at the 6,000-psi, 10,000-psi, and 14,000-psi levels. Significant differences were detected at the 8,000-psi and 12,000-psi levels. In the 8,000-psi group, ground ends produced significantly lower compressive strengths than three of the capping compounds. For the 12,000-psi group, ground ends produced significantly lower strengths than one of the capping compounds and the unbonded pads. In all strength levels but the 6,000-psi level, the ground ends method produced lower average compressive strengths than the other methods studied. These results imply the viability of alternative methods of end treatments such as unbonded pads and capping compounds for use with HSC.

Capping Systems for High-Strength Concrete

This study focused on the effects of capping systems on the compressive strength of high-strength concrete (HSC). The three systems investigated were ground ends, bonded caps, and unbonded pads. Five compressive strength groups were examined with strength levels ranging from 6,000 psi to 14,000 psi. The capping compounds investigated were commercially available and advertised for testing HSC. The unbonded pads were neoprene pads with a Shore A Durometer hardness of 70. A grinding machine was used to obtain the required planeness and perpendicularity on the ground end cylinders. No significant difference was found between the capping systems at the 6,000-psi, 10,000-psi, and 14,000-psi levels. Significant differences were detected at the 8,000-psi and 12,000-psi levels. In the 8,000-psi group, ground ends produced significantly lower compressive strengths than three of the capping compounds. For the 12,000-psi group, ground ends produced significantly lower strengths than one of the capping compounds and the unbonded pads. In all strength levels but the 6,000-psi level, the ground ends method produced lower average compressive strengths than the other methods studied. These results imply the viability of alternative methods of end treatments such as unbonded pads and capping compounds for use with HSC.

Damage mitigation by innovative materials for Temple C at Selinunte

Greek temples are made of overlapped heavy stone blocks shaped to form columns and entablatures. Preservation of these constructions requires specific structural engineering effort. Present conditions of remains basically reflect centuries of loads and environmental actions, but also undesired effects of former restorations. The latter, if not properly designed, may affect the value and life expectation of these monuments. In the present paper, a novel interpretation of the jacketing technique for temporary interventions and the application to the Greek Temple C of the Selinunte’s (Sicily) archaeological site are presented. Purpose of jacketing is to avoid worsening of the crack pattern by light confinement of stone blocks. Titanium belts and elastomeric neoprene pads are combined to attain the above-mentioned performances. Simplified design model is proposed and a 3D finite elements analysis is performed to evaluate local effects of jacketing; finally information about in situ application are given.

대형 잔향실의 방진 구조 설계 및 검증시험

A vibration isolation system for a large reverberation chamber (1,228 <TEX>$m^3$</TEX> and 1,000 ton) has been installed and verified. The reverberation chamber generates loud noise and induces high level of vibration while performing spacecraft acoustic reliability tests. The isolation system prevents vibration transfer from the chamber to the enclosure buildings. This paper describes design process and commissioning experiments of the system. Design criteria have been derived from rigid body model of the chamber. The stiffness of neoprene pads has been selected by employing finite element analysis of the reverberant chamber and isolation system. A total of 21 neoprene pads have been installed between the chamber and supporting Pedestals. A sand bag of 800kg was dropped on the chamber floor to measure the natural frequency of the isolation system. While 136.9 dB noise is generated in the chamber, absolute transmissibility of the isolation system has been measured. The measured natural frequency of the chamber is 10.2Hz, which is 80% of the predicted value. Overall transmissibility at working frequency range (25∼10.000 Hz) is less than -12.4 dB.

A New Unbonded Capping Practice for Evaluating the Compressive Strength of Controlled Low-Strength Material Cylinders

Abstract Controlled Low-Strength Material (CLSM) is a low strength cementitious material often used for pipe bedding, backfill, void fills, and in some cases bridges approaches. Because of its low strength, handling of test cylinders, especially at early ages, is often not possible or results in significant damage to the samples. Sulfur-capped specimens require more handling than non-sulfur capped specimens. To minimize handling, a new material is proposed for use as an end pad for compressive strength testing. Similar to the approach used for conventional concrete cylinders, a new method is proposed that uses different pads for different CLSM compressive strength levels. Pads made of sorbothane viscoelastic polyurethane rubber, neoprene, and a combination of the two were used for compressive strength and variability. Results indicate that the sorbothane viscoelastic polyurethane rubber material should be used when the compressive strength of the CLSM is less than approximately 1 MPa and neoprene pads with a durometer value not greater than 50 should be used when the compressive strength is expected to be greater than 2 MPa. Either pad type can be used for CLSM mixtures having expected compressive strengths between 1.0 and 2.0 MPa.

Alternative Cap Materials for Evaluating the Compressive Strength of Controlled Low-Strength Materials

This research investigated the influence of different capping materials on the compressive strength of controlled low-strength material (CLSM). These capping materials included a sulfur compound, gypsum capping compound, and neoprene pads with different durometer hardness values. Neoprene pads with Shore A durometer hardness values of 20, 40, 50, 60, and 70 were incorporated into the test program. A total of eight CLSM mixtures that covered a wide range of mixture compositions was included in this study. Sulfur capping compound was found to generate the most consistent compressive strength values and was thus used as a control in qualifying other capping materials. With a slightly modified ASTM C 1231 procedure, neoprene pads with a Shore A durometer value equal to or less than 50 were qualified to yield compressive strength values not less than 80% of the corresponding value from the sulfur mortar capping compound results at a significance level of 5%, as required in ASTM D 4832. At this same level of significance, the compressive values from CLSM cylinders capped with gypsum capping compound were found to be more than 92% of the control values from the sulfur mortar capped cylinder results. But, this capping procedure was found to be more time consuming than the neoprene pad testing. As such, sulfur capping compound and neoprene pads with a Shore A durometer value of not more than 50 are recommended to evaluate the compressive strength of CLSM cylinders.

An Improved Capping Technique for Excavatable Controlled Low Strength Material Compressive Strength Cylinders

Abstract ASTM D 4832: Standard Test Method for Preparation and Testing of Controlled Low Strength Material (CLSM) Test Cylinders currently permits three types of capping for CLSM cylinders: sulfur mortar (ASTM C 617), gypsum plaster (ASTM C 617), and unbonded neoprene restrained by rigid retainers (ASTM C 1231). These cappings were developed for portland cement concrete (PCC) cylinders and all produce good estimates of PCC potential strength. However, these cappings are inappropriate for excavatable CLSM cylinders. Sulfur mortar and gypsum plaster methods often result in cylinder damage during capping due to the low strength of excavatable CLSM cylinders. The recommended 50 to 70 durometer neoprene pads are far too stiff at low stress levels, which are common in testing excavatable CLSM cylinders. The neoprene pads essentially act as a rigid plate rather than a capping material. The authors developed an unbonded capping system using a much softer neoprene that is more malleable at lower stress levels. To evaluate the effectiveness of the new capping system, ten batches of an air-entrained and ten batches of a non-air-entrained excavatable CLSM were produced. Each batch was approximately 0.0453-m3, allowing 20 100-by-200 mm cylinders as well as flow consistency (ASTM D 6103) and gravimetric air tests (ASTM D 6023). Five pairs of cylinders were tested at 7 days and five pairs at 28 days. At each age, one pair was capped with each of the following materials: sulfur mortar, gypsum plaster, 50-durometer neoprene, nothing, and the new softer neoprene unbonded capping system. The average 28-day compressive strength of the cylinders using the proposed capping system was 275 kPa (39.83 psi) for non-airentrained and 345 kPa (50.01 psi) for the air-entrained mix design. The proposed capping system was not significantly different than the sulfur mortar or gypsum plaster. It was significantly superior to 50-plaster durometer neoprene and the no-cap technique.

Efficiency of helical springs and viscodampers in base isolation

Results of an experimental testing are presented for a five-storey steel frame model, subjected to horizontal and vertical earthquake vibrations with varying intensities. The dynamic testing included the fixed base conditions, as well as full isolation by means of neoprene pads and helical springs, coupled with or without viscous dampers. The response of the structural model to both horizontal and vertical vabrations has been thoroughly recorded, and these records have been correlated with those of the analytical investigations. The main conclusion of the study is that the vertical vibrations may unexpectedly cause response amplifications at very high undesirable levels, especially when the structure is base isolated by means of rubber pads. No such deficiency occurs, however, when helical springs and viscodampers are used.

Effects of Testing Variables' Effects on the Comparison of Ceoprene Pad and Sulfur Mortar-Capped Concrete Test Cylinders

The paper compares the compressive strength of 127 pairs of 6 x 12 in. concrete cylinders capped with neoprene pads restrained by aluminum caps to compressive strengths of cylinders capped with a traditional sulfur mortar compound. Twelve testing variables were examined to determine whether the two capping methods would give similar results under different testing conditions. Although neoprene caps gave significantly different results from the sulfur caps for several testing variables, the results were not significantly different from the mean of the sulfur-capped specimens when proper ASTM procedures were followed for molding and testing cylindrical specimens.

Behavior and Design of Selected Elastomeric Bearing Pads

e general objective of this project was the determination of the behavior of elastomeric bearing pads under monotonic or cyclic compression, cyclic shear and rotation, or combinations of these loading conditions. Two types of bearing pads were tested, random oriented fiber (ROF) pads and Neoprene pads of AASHTO grade. A summary of the test reports supplied with these pads has been included in Appendix A. These pads are intended for general use under stemmed members or beams in the precast concrete industry. The scope of the project can best be defined by describing the parameters

Neoprene Pads for Capping Concrete Cylinders

Abstract This study investigated the feasibility of using neoprene pads confined by steel end caps instead of sulfur-mortar caps in compressive strength tests on 150- by 300-mm (6- by 12-in.) concrete cylinders. The 13-mm (½-in.) thick neoprene pads had a 50 durometer hardness and were cut to fit in the end caps, which had an inside diameter of 159 mm (6¼ in.) with a tolerance of +0 and −2 mm (−1/16 in.). Compressive strength data were obtained from 438 pairs of cylinders prepared in the field from commercial batches of concrete. One cylinder of each pair was tested with neoprene pads and the other with sulfur-mortar caps. Although the results indicate statistically significant differences in the values obtained by the two capping methods, the differences are considered negligible from a practical standpoint. A linear regression analysis indicated a good correlation between the two methods.

Seismic isolation using sliding-elastomer bearing pads

Seismic isolation of nuclear power plants using sliding-elastomer bearing pads is reviewed. The foundation system involves a double raft interposed with reinforced neoprene pads and friction plates. All safety related structures are founded on the common (or connected) upper raft(s) which is in turn supported by a common lower raft founded on the subsurface soils. The pads act as a filter between the primary structures and the ground, limiting the horizontal earthquake forces and accelerations experienced by the structures. The low natural frequency of the predominant horizontal mode minimizes participation of higher structural modes. The performance and reliability of the system is demonstrated from the results of shaking table tests of scaled models, load and environmental tests of the bearings and various analytical studies. The characteristic features of the aseismic foundation system is shown to offer a number of advantages over conventionally designed structures in terms of performance, cost and safety. The system has been developed by Spie-Batignolles Bâtiment Travaux Publics in collaboration with Electricité de France, and has been incorporated into the design of a number of nuclear power plants.