Steel Cold-formed Trussed Girders with Joint Eccentricities - Improvements on Design and Performance by Numerical and Experimental Analysis

Long span light roof systems of industrial buildings are frequently designed with cold-formed steel members, leading to competitive solution which allows liberating useful internal space inside the building. This type of structural solution is usually cost saving if it is combined with standardization of the manufacturing process thus enabling specialized solution. This is the case of a family of trussed girders ranging from 0.6 to 1.8 m depth, developed by the steel structures manufacturer and addressed to a standard system for general application enabling to bridge up to 40 m span of light roof construction. Typical buckling behavior of the cold-formed members, with special emphasis to the unsymmetrical stiffened Z section chord members was investigated as well as the effect of the eccentricities in the joints. Numerical and experimental results allowed understanding the buckling behavior of these members as well as confirming its strength capacity. For this both axially compressed tests of the Z chord member and load test of a complete trussed beam were performed and the obtained results were applied to improve the structural design. The comparison between experimental results and those from the prescriptions of the Brazilian design code addressed to steel cold-formed structural members (direct strength method-based strength check) will be presented and commented. The obtained results allowed confirming the actual behavior and ultimate loading condition of the trussed girder

Effect of storage period on the accuracy of elastomeric impressions

AIMS: To investigate the effect of the storage period on the accuracy of recently developed elastomeric materials. METHODS: Simultaneous impressions of a steel die were taken using a polyether (I: Impregum Soft Heavy and Light body, 3M ESPE) and vinyl polysiloxane (P: Perfectim Blue Velvet and Flexi-Velvet, J.Morita). The trays were loaded with the heavy-bodied impression materials while the light-bodied impression materials were simultaneously spread on the steel die. The impressions were poured after 2 hours, 24 hours, and 7 days. Impressions were stored at approximately 55% relative humidity and room temperature. Ten replicas were produced for each experimental condition (n=60). Accuracy of the stone dies was assessed with a depth-measuring microscope. The difference in height between the surface of the stone die and a standard metallic ring was recorded in micrometers at four demarcated points, by two independent examiners. Data were submitted to two-way ANOVA and Tukey test (a = 0.05). RESULTS: Significant differences were found among the groups. Smaller discrepancies were observed when pouring was performed up to 24 hours (I-2h= 65.0 ± 15.68 µm; I-24h= 81.6 ± 11.13 µm) for the polyether, and up to 7 days for the vinyl polysiloxane (P-2h= 79.1 ± 13.82 µm; P-24h= 96.8 ± 6.02 µm; P-7d= 81.4 ± 4.3 µm). Significant dimensional discrepancies, however, were observed when polyether was stored for 7 days (I-7d= 295.3 ± 17.4 µm). CONCLUSION: Storage may significantly affect the dimensional accuracy of impressions and, thus, a maximum period and storage condition should be specified for the recently developed materials

Strategic Sourcing : A supply Chain Perspective

Exam paper for first semester 201

Effect of light-curing units and activation mode on polymerization shrinkage and shrinkage stress of composite resins

The aim of this study was to evaluate the polymerization shrinkage and shrinkage stress of composites polymerized with a LED and a quartz tungsten halogen (QTH) light sources. The LED was used in a conventional mode (CM) and the QTH was used in both conventional and pulse-delay modes (PD). The composite resins used were Z100, A110, SureFil and Bisfil 2B (chemical-cured). Composite deformation upon polymerization was measured by the strain gauge method. The shrinkage stress was measured by photoelastic analysis. The polymerization shrinkage data were analyzed statistically using two-way ANOVA and Tukey test (p<0.05), and the stress data were analyzed by one-way ANOVA and Tukey's test (p<0.05). Shrinkage and stress means of Bisfil 2B were statistically significant lower than those of Z100, A110 and SureFil. In general, the PD mode reduced the contraction and the stress values when compared to CM. LED generated the same stress as QTH in conventional mode. Regardless of the activation mode, SureFil produced lower contraction and stress values than the other light-cured resins. Conversely, Z100 and A110 produced the greatest contraction and stress values. As expected, the chemically cured resin generated lower shrinkage and stress than the light-cured resins. In conclusion, The PD mode effectively decreased contraction stress for Z100 and A110. Development of stress in light-cured resins depended on the shrinkage value

Effect of light-curing units and activation mode on polymerization shrinkage and shrinkage stress of composite resins

The aim of this study was to evaluate the polymerization shrinkage and shrinkage stress of composites polymerized with a LED and a quartz tungsten halogen (QTH) light sources. The LED was used in a conventional mode (CM) and the QTH was used in both conventional and pulse-delay modes (PD). The composite resins used were Z100, A110, SureFil and Bisfil 2B (chemical-cured). Composite deformation upon polymerization was measured by the strain gauge method. The shrinkage stress was measured by photoelastic analysis. The polymerization shrinkage data were analyzed statistically using two-way ANOVA and Tukey test (

Avaliação in vitro da resistência de união de diferentes combinações entre adesivos e resinas compostas

The aim of this work was to evaluate the in vitro compatibility between some composite resins (Herculite XR, Z100 and AP.H) and different adhesives (XR-Bond, Scotchbond MP and PUB3), since for various reasons, the utilization of composite resins and adhesives from different commercial brands is very frequent in the dental practice. We used a device constituted of a base and a matrix which, when juxtaposed, showed a cavity in dumbbell shape which received the composite resin. Firstly, 45 half-specimens of each composite resin were made and stored in distilled water at 37ºC for one week. Then, they were replaced in the matrix for the building of the second half and divided into groups to combine each composite resin with each one of the three adhesives. The specimens were stored in distilled water at 37ºC and after the period of 7 days they were submitted to the tensile strength test in a Kratos machine. It was concluded that: generally, the composite resins and the adhesives showed to be compatible; the combination AP.H/XR-Bond showed the highest discrepancy, since the tensile strength was statistically smaller than that of the combination proposed by the manufacturer; the other combinations of the adhesives and the composite resins showed tensile strengths statistically similar to or greater than that of the combination recommended by the manufacturer.O objetivo desta pesquisa foi avaliar in vitro a compatibilidade entre as resinas compostas Herculite XR, Z100, AP.H e os diferentes adesivos XR-Bond, Scotchbond MP e PUB 3, uma vez que, por uma série de motivos, é muito freqüente na prática clínica do cirurgião-dentista a utilização de resina e adesivo de marcas comerciais diferentes. Utilizou-se um dispositivo constituído de base e matriz, as quais, quando justapostas, apresentavam uma cavidade em forma de halteres que recebeu a resina composta. Inicialmente, confeccionaram-se 45 meio-espécimes de cada resina. Após uma semana armazenados em água destilada a 37ºC, os meio-espécimes foram reposicionados na matriz para confecção da segunda metade e divididos em grupos de modo a combinar cada resina com cada um dos três adesivos. Armazenaram-se os espécimes em água destilada a 37ºC por 7 dias e procedeu-se ao teste de tração na máquina Kratos. Concluiu-se que: de forma geral, as interações entre as resinas e os adesivos testados mostraram-se compatíveis; a combinação AP.H/XR-Bond apresentou a maior discrepância, pois a resistência à tração foi estatisticamente inferior à associação original proposta pelo fabricante; as demais combinações entre os adesivos e as resinas testadas apresentaram resistência à tração estatisticamente semelhantes ou superiores à associação recomendada pelo fabricante

Influence of pulse-delay curing on sorption and solubility of a composite resin

The purpose of this study was to evaluate the sorption and solubility of a composite resin (TPH³; Dentsply) cured with halogen light due to different storage media and curing modes. The methodology was based on the ISO 4049 standard. Two independent groups were established according to the storage time (7 days-G1; 60 days-G2). A stainless steel mould (2 mm x 8 mm Ø) was used. The selected curing modes were: I (Conventional - C): 40s - 600 mW/cm²; II (Pulse I - PD): 3 s - 200 mW/cm² + 2 min (delay) + 39 s - 600 mW/cm²; III (Pulse II): 10 s - 200 mW/cm² + 2 min (delay) + 37 s - 600 mW/cm²; IV (Pulse III): 3 s- 600 mW/cm² + 2 min (delay) + 37 s -600 mW/cm². The media used were: distilled water, 75% ethanol and 100% chlorophorm. Five repetitions were made for each group. The specimens were placed in a desiccator at 37ºC for 24 h and, after that, at 23ºC for 1 h to be weighed until a constant mass (m1) was obtained. The discs were immersed separately into the 3 media for 7 days (G1) and 60 days (G2), and thereafter reweighed (m2). The reconditioning in the desiccator was done until a constant mass (m3) was obtained. Sorption and solubility were calculated and the data of G1 and the sorption data of G2 were subjected to two-way ANOVA and Tukey's tests (p=0.05). The solubility data of G2 were analyzed by Kruskal-Wallis test (p=0.05). For G1 and G2, no statistically significant differences were found in sorption among curing techniques (p>;0.05). The solubility values were negative, which means that there was mass gain. Regarding the storage media, in G2 chlorophorm had the highest sorption values. It may be concluded that the curing modes (C and PD I, II and III) did not affect the sorption of the tested composite resin. However, different storage media influenced sorption behavior. The solubility test demonstrated negative data, masking the real solubility

Influence of pulse-delay curing on sorption and solubility of a composite resin

The purpose of this study was to evaluate the sorption and solubility of a composite resin (TPH³; Dentsply) cured with halogen light due to different storage media and curing modes. The methodology was based on the ISO 4049 standard. Two independent groups were established according to the storage time (7 days-G1; 60 days-G2). A stainless steel mould (2 mm x 8 mm Ø) was used. The selected curing modes were: I (Conventional - C): 40s - 600 mW/cm²; II (Pulse I - PD): 3 s - 200 mW/cm² + 2 min (delay) + 39 s - 600 mW/cm²; III (Pulse II): 10 s - 200 mW/cm² + 2 min (delay) + 37 s - 600 mW/cm²; IV (Pulse III): 3 s- 600 mW/cm² + 2 min (delay) + 37 s -600 mW/cm². The media used were: distilled water, 75% ethanol and 100% chlorophorm. Five repetitions were made for each group. The specimens were placed in a desiccator at 37ºC for 24 h and, after that, at 23ºC for 1 h to be weighed until a constant mass (m1) was obtained. The discs were immersed separately into the 3 media for 7 days (G1) and 60 days (G2), and thereafter reweighed (m2). The reconditioning in the desiccator was done until a constant mass (m3) was obtained. Sorption and solubility were calculated and the data of G1 and the sorption data of G2 were subjected to two-way ANOVA and Tukey's tests (p=0.05). The solubility data of G2 were analyzed by Kruskal-Wallis test (p=0.05). For G1 and G2, no statistically significant differences were found in sorption among curing techniques (p>0.05). The solubility values were negative, which means that there was mass gain. Regarding the storage media, in G2 chlorophorm had the highest sorption values. It may be concluded that the curing modes (C and PD I, II and III) did not affect the sorption of the tested composite resin. However, different storage media influenced sorption behavior. The solubility test demonstrated negative data, masking the real solubility

Evaluation of internal adaptation of Class V resin composite restorations using three techniques of polymerization

OBJECTIVE: The purpose of this in vitro study was to evaluate the internal adaptation of Class V composite restorations to the cavity walls using three different techniques of polymerization. METHODS: Standard cavities were prepared on the buccal and lingual surfaces of 24 extracted human third molars with margins located above and below the cementoenamel junction. Restorations were placed in one increment using two restorative systems: 3M Filtek A110/ Single Bond (M) and 3M Filtek Z250/ Single Bond (H) in the same tooth, randomly in the buccal and lingual surfaces. Resin composites were polymerized using three techniques: Group 1 - Conventional (60 s - 600 mW/cm²); Group 2 - Soft-start (20 s - 200 mW/cm² , 40 s - 600 mW/cm²); Group 3 - Pulse Activation (3 s - 200 mW/cm², 3-min hiatus, 57 s - 600 mW/cm²). Buccolingual sections were polished, impressions taken and replicated. Specimens were assessed under scanning electron microscopy up to X1000 magnification. Scores were given for presence or absence of gaps (0 - no gap; 1 - gap in one wall; 2 - gap in two walls; 3 - gap in three walls). RESULTS: The mean scores of the groups were (±SD) were: G1M-3.0 (± 0.0); G2M-2.43 (± 0.8); G3M- 1.71 (± 0.9); G1H- 2.14 (± 1.2); G2H- 2.00 (± 0.8); G3H- 1.67 (± 1.1). Data were analyzed using Kruskal-Wallis and Dunnet's tests. No statistically significant difference (p>;0.05) was found among groups. Gaps were observed in all groups. CONCLUSIONS: The photocuring technique and the type of resin composite had no influence on the internal adaptation of the material to the cavity walls. A positive effect was observed when the slow polymerization techniques were used

Avaliação clínica de restaurações de lesões cervicais não cariosas

The purpose of this study was to assess the clinical performance of bonded composite (Excite/Tetric Ceram - Vivadent) versus a resin-modified glass ionomer cement (Vitremer - 3M) for restoring non-carious cervical lesions. A total of 70 restorations (thirty-five per material) were placed in 30 patients, 18-50 aged, by one operator. Rubber dam was employed in all cases, lesions were pumiced, enamel margins were not beveled, and no mechanical retention was placed. The restorations were directly assessed by two independent evaluators using modified-USPHS criteria for six clinical categories. The ratings for clinical acceptability restorations (alfa plus bravo) were as follows (Tetric Ceram/Vitremer): retention (86%/100%), marginal integrity (100%/100%), marginal discoloration (100%/100%), wear (97%/100%), postoperative sensitivity (100%/100%) and recurrent caries (100%/100%). Statistical analysis was completed with Fisher's exact or Pearson Chi-square tests at a significance level of 5% (PAvaliou-se o desempenho clínico de um sistema restaurador adesivo (Excite - Tetric Ceram/ Vivadent) e do cimento de ionômero de vidro modificado por resina (Vitremer/ 3M) na restauração de lesões cervicais não cariosas por meio do sistema de avaliação do USPHS modificado. Um total de setenta restaurações, trinta e cinco por material, foi realizado por um único operador em trinta pacientes voluntários com idades de 18 a 50 anos. Previamente à execução das restaurações, foi realizada uma profilaxia com pedra-pomes e água a fim de remover quaisquer resíduos. As lesões cervicais não foram submetidas a qualquer tipo de preparo cavitário, sendo restauradas sob isolamento absoluto e de acordo com as instruções do fabricante. Todas as restaurações foram avaliadas pelo método direto por dois examinadores usando os critérios de retenção (R), integridade marginal (IM), descoloração marginal (DM), desgaste (D), sensibilidade pós-operatória (S) e incidência de cárie (IC). Ao final de um ano, os resultados de restaurações clinicamente satisfatórios (escores Alfa e Bravo) obtidos para resina composta e cimento de ionômerto de vidro modificado por resina foram respectivamente: R (86%/100%), IM (100%/100%), DM (100%/100%), D (97%/100%), S (100%/100%) e IC (100%/100%). Os resultados foram submetidos à análise estatística com o teste exato de Fisher ou o teste Qui-quadrado de Pearson com o nível de significância de 5% (