Case Study of Strength Calculation and the Possible Repair Options for Screw Thread Damages

Thread Strength and repair capability are critical to successful screw joints for any mechanical assembly. This paper explores the effect of the thread damage utilizing hand calculations, the margin of safety (MOS) for internal & external threads and compares with the required design criteria limit. Hence, the reduction in thread capability is analyzed in terms of shear and bearing strength of threads. This paper also emphasizes the Industry-standard repair techniques such as Helical inserts, Oversize inserts, and Twinserts with limitations and expected process/techniques. Advanced thread repairs in the market such as solid-body thread inserts (key-style, Time-sert, Big-sert) are also discussed Keywords: Thread damages, Shear strength, bearing strength. STI (Screw thread insert)

Effect of Glass Fiber Hybridization on the Durability in Salt-Fog Environment of Pinned Flax Composites

The aim of the present paper is to evaluate the effect of the hybridization with external layers of glass fibers on the durability of flax fiber reinforced composites in severe aging conditions. To this scope, full glass, full flax and hybrid glass–flax pinned laminates were exposed to a salt-fog environment for up to 60 days. Double-lap pinned joint tests were performed to assess the pin-hole joints performances at varying the laminate stacking sequence. In order to better discriminate the relationship between the mechanical behavior and the fracture mechanisms of joints at increasing the aging time, different geometries (i.e., by varying both the hole diameter D and the free edge distance from the center of the hole E) were investigated after 0 (i.e., unaged samples), 30 and 60 days of salt-fog exposition. It was shown that the hybridization positively affects the mechanical performance as well as the stability of pinned composites: i.e., improvements in both strength and durability against the salt-fog environment were evidenced. Indeed, the hybrid laminate exhibited a reduction in the bearing strength of about 20% after 60 days of aging, despite to full flax laminate, for which a total reduction in the bearing strength of 29% was observed. Finally, a simplified joint failure map was assessed, which clusters the main failure mechanisms observed for pinned composites at varying aging conditions, thus assisting the joining design of flax–glass hybrid laminates.

Perbaikan dan Perkuatan Fondasi Tiang Bor pada Bangunan Gedung Perkuliahan dengan Penambahan Tiang Pancang Bulat

Fondasi harus dibangun di atas tanah keras agar bangunan tetap stabil dan kokoh. Memastikan kekuatan fondasi adalah upaya dini untuk mencegah sudden collapse pada bangunan di kemudian hari. Penelitian ini dilakukan untuk mengetahui kuat dukung tanah pada ujung tiang fondasi dan mengamati sejauh apa kerusakan beton tiang bor pada bangunan yang baru masih dalam tahap pembangunan fondasi. Data penelitian diperoleh dari hasil pengujian PDA (Pile Driving Analyzer) dan PIT (Pile Integrity Test) pada fondasi bangunan jenis bored pile D80. Pada gedung yang berdekatan, yang dikerjakan dengan sistem yang sama dan menggunakan spun pile D50. Data kuat dukung ultimate hasil manometer alat uji hidraulik 175 ton untuk pile D50. Dari analisis uji PDA, diperoleh nilai kuat dukung ijin rata-rata tiang bor adalah 70,25 ton (51%). Analisis ulang terhadap kombinasi beban menghasilkan tambahan spun pile di 44 titik. Pada beton bored pile yang mengalami kerusakan, dilakukan perbaikan seperti penambahan cor pada lapisan luar (concrete-jacketing) untuk menutupi lapisan tulangan yang terekspos, dan penambahan tulangan terpisah di sisi dalam beton untuk antisipasi bila tulangan luar rusak akibat korosi.The foundation must be placed on hard rock so that the building remains stable and solid. Thus, ensuring the strength of the foundation is an early effort to prevent sudden collapse of the building in the future. This research was conducted to determine the bearing strength of the soil at the ends of the foundation piles and to observe the extent of the damage to the drill pile concrete in the new building which is still in the foundation construction stage. The research data were obtained from the results of PDA (Pile Driving Analyzer) and PIT (Pile Integrity Test) testing on the foundation of the bored pile type D80 building. The adjacent building is being worked on with the same system and using a D50 spun pile. With the ultimate bearing strength data, the results of the hydraulic tool manometer = 175 tons for D50 piles. PDA test analysis obtained the average allowable bearing strength of the drill pile is 70.25 tons (51%). The re-analysis of the load combination resulted in additional spun piles at 44 points. In the damaged bored pile concrete, namely by adding cast to the outer layer (concrete-jacketing) to cover the exposed reinforcement layer, and adding separate reinforcement on the inside of the concrete to anticipate if the outer reinforcement is damaged due to corrosion.Fondasi harus dibangun di atas tanah keras agar bangunan tetap stabil dan kokoh. Memastikan kekuatan fondasi adalah upaya dini untuk mencegah sudden collapse pada bangunan di kemudian hari. Penelitian ini dilakukan untuk mengetahui kuat dukung tanah pada ujung tiang fondasi dan mengamati sejauh apa kerusakan beton tiang bor pada bangunan yang baru masih dalam tahap pembangunan fondasi. Data penelitian diperoleh dari hasil pengujian PDA (Pile Driving Analyzer) dan PIT (Pile Integrity Test) pada fondasi bangunan jenis bored pile D80. Pada gedung yang berdekatan, yang dikerjakan dengan sistem yang sama dan menggunakan spun pile D50. Data kuat dukung ultimate hasil manometer alat uji hidraulik 175 ton untuk pile D50. Dari analisis uji PDA, diperoleh nilai kuat dukung ijin rata-rata tiang bor adalah 70,25 ton (51%). Analisis ulang terhadap kombinasi beban menghasilkan tambahan spun pile di 44 titik. Pada beton bored pile yang mengalami kerusakan, dilakukan perbaikan seperti penambahan cor pada lapisan luar (concrete-jacketing) untuk menutupi lapisan tulangan yang terekspos, dan penambahan tulangan terpisah di sisi dalam beton untuk antisipasi bila tulangan luar rusak akibat korosi.

Analysis of Bearing Strength of Post-Tensioning Anchorage Zone with Respect to Relative Bearing Area and Lateral Confinement Design

This study aimed to evaluate the bearing strength of the post-tensioning anchorage zone with respect to the relative bearing area and lateral confinement design of spiral and stirrup rebars. Eleven specimens were fabricated and tested to fracture in accordance with EAD 160004-00-0301. Load-displacement curves and fracture modes were analyzed. Then, the conventional design equation for the bearing strength and previous findings on the relative bearing area was re-investigated in comparison with the test results. From the test, the representative findings are as follows: (1) A specimen with relatively small size and less lateral reinforcement is more likely to be affected by the wedge action of the anchorage device; however, a larger specimen is affected by both concrete crushing and/or spalling; (2) The behavior of the anchorage zone is markedly affected by the local behavior near the anchorage bearing plate, and the sectional efficiency is mostly determined by A/Ag; (3) For specimens with A/Ag = 9.52, the proportional limit of the load-displacement curve is determined by the yield of spiral rebar or fracture of the bearing plate, but the later part of the curve is determined by lateral confinement; (4) The maximum A/Ag that could produce 100% sectional efficiency is about 2.0 for the anchorage bearing plate used in the test; (5) For a fully confined specimen with a small-diameter spiral for minimum anchorage spacing, the stirrup rebar design mainly influences crack occurrence and patterns when the size of the specimen is equal to the minimum anchorage spacing; however, the area of the load-displacement curve after the proportional limit as well as crack occurrence and patterns are also influenced by stirrup rebar design when A/Ag is relatively large; (6) Finally, a revised design model is proposed to effectively estimate the ultimate bearing strength of the post-tensioning anchorage zone without respect to A/Ag. From the comparison of the design equations, it was concluded that the proposed equation provides a more reliable prediction with a 14.0% average error rate and 5.7% standard deviation of error rate.

Improving Soil Properties by Using Coir

Construction on these soils is found to be expensive because of their low bearing strength. Soil having poor bearing need stabilization to make it suitable for construction purpose. In this study coir (extracted from coconut) is used as natural fiber for stabilization of soil. Stabilization using natural fiber is a cost-effective and eco-friendly approach to improve properties of soil. The study is carried out to evaluate the effects of coir fiber on properties of soil. Coconut coir in the soil were varied from 0, 0.5, 1.0, 1.5, and 2.0% and various soil properties were studied.