Theoretical Study on the Flexural Behavior of Structural Elements Strengthened with External Pre-Stressing Methods

This study aims to strengthen the flexural behavior of structural elements with external pre-stressing tendons, thereby improving their load-carrying capacity and increasing their resistance against the external load. Different techniques were used to apply external pre-stressed strengthening to RC beams and RC frames. Seven identical RC frames were analyzed: an original sample without an external tendon, two strengthened samples with external tendons at the positive bending zone, two strengthened samples with external tendons at the beam–column connection zone, a strengthened sample with external straight line tendons along the beam and, finally, a strengthened sample with external U-shape tendons along the beam of the frame. The analysis and the results were obtained using ANSYS WORKBENCH finite element (FE) program. Comparisons were performed between these techniques to determine which technique is better for strengthening. The failure mode, vertical deflection, column stress, load-carrying capacity, and ductility of the samples were listed and analyzed under four-point vertical loading. The results show that using external tendons significantly increases the load capacity and the stiffness of structural frames. Moreover, the tendon in the beam zone is more effective than the tendon in the column zone.

Biomechanical Analysis of Running in Shoes with Different Heel-to-Toe Drops

The heel-to-toe drop of running shoes is a key parameter influencing lower extremity kinematics during running. Previous studies testing running shoes with lower or larger drops generally used minimalist or maximalist shoes, where the factors outside of the drop may lead to the observed changes in running biomechanics. Therefore, our aim was to compare the strike patterns, impact force, and lower extremity biomechanics when running in shoes that varied only in their drops. Eighteen habitual rearfoot strikers performed trials wearing running shoes with four drop conditions: 15 mm, 10 mm, 5 mm, and without a drop. Three-dimensional (3D) tracks of the reflective markers and impact force were synchronously collected using a video graphic acquisition system and two force plates. The biomechanical parameters were compared among the four drop conditions using one-way ANOVA of repeated measures. A greater foot inclination angle (p = 0.001, ηp2 = 0.36) at initial contact and a lower vertical loading rate (p = 0.002, ηp2 = 0.32) during the standing phase were found when running in shoes with large drops compared with running in shoes without a drop. Running in shoes with large drops, as opposed to without, significantly increased the peak knee extension moment (p = 0.002, ηp2 = 0.27), but decreased the peak ankle eversion moment (p = 0.001, ηp2 = 0.35). These findings suggest that the heel-to-toe drop of running shoes significantly influences the running pattern and the loading on lower extremity joints. Running shoes with large drops may be disadvantageous for runners with knee weakness and advantageous for runners with ankle weakness.

New Recommendations for Offshore Wellhead Platform Structural Design Due to Well Conductor Casings Failures: Outcome of a Study Based on Actual Findings

Detailed study on structurally failed well conductors on offshore wellhead platforms lead us to believe that existing assumptions of conductors transfer only lateral loadings to wellhead platforms while entire well vertical loading will be carried by conductor itself; could be wrong. The well conductors could become ‘forced’ to carry a very large vertical loads incase the conductors are structurally failed; especially once exceeded its original design life. As such, some new considerations during the wellhead platform design, which need to be followed, are recommended here. These are to cater any catastrophic eventuality of conductor failures which will restrain further collapse of the conductors or to avoid any progressive collapse of the platform. The recommendations are from a study based on actual findings observed recently in the offshore field. The connection between conductors and platforms are conventionally designed as guided based on the load transfer assumptions. That is the huge vertical loadings from internal conductor casings and associated items were not a concern for platform design structural engineers, traditionally, and as such the conductors were designed to be structurally connected to the wellhead platforms using vertical guides. Due to extended design service life of platforms, in many cases the design life went up to two times of their original design life, severe degradation of structural integrity of the conductors were observed in the field. Structural analysis and assessment were carried out on many old intact and failed conductors, in the offshore field, in order to assess its structural and loading behavior with respect to supporting wellhead platforms. The study provided that the failed conductors were leaning / collapsing to the wellhead platform resulting in transferring a huge vertical loads which originally were designed to be carried by conductors alone. This huge transfer of vertical loads from conductor to the platform was unexpected and was not considered in platforms original design. Therefore, the platform should have sufficient structural strength to cater such extreme eventuality to avoid the risk of complete collapse. A risk assessment of a tilted / failed conductors indicated that the consequence of total failure of a conductor could be catastrophic in case the platform failed to resist the collapsing conductors. This paper presents the details of the study carried out on aged wellhead platforms, having failed long serving conductors, in Giant offshore field, Abu Dhabi, along with details of new recommendations to be followed while designing new wellhead platforms. The paper also recommends the structural design consideration to be followed while designing wellhead platforms in-case a conductor repair is necessitated in future.

Effect of Moisture Content on the Mechanical Properties of Watermelon Seed Varieties

The effect of moisture content on the mechanical properties of agricultural material is essential during design and adjustment of machines used during harvest, cleaning, separation, handling and storage. This study determined some mechanical properties of Black and Brown colored of watermelon seed grown in Nigeria under different moisture contents range of 6.5 to 27.8% (d.b). The results for the mechanical properties obtained ranged from 15.68-29.54 N for compressive force; 1.95-3.40 mm for compressive extension; 0.13-0.33 N mm-2 for compressive strength; and 0.17-1.93 kJ for deformation energy at vertical loading position while at horizontal loading position, results obtained ranged from 14.71-38.36 N for compressive force; 1.94-4.20 mm for compressive extension; 0.16-0.32 N mm-2 for compressive strength; and 1.47-76.39 kJ for deformation energy for Black colored watermelon seed. The compressive force, compressive extension, compressive strength, deformation energy ranged from 14.18-36.49 N, 1.85-5.20 mm, 0.19 0.76 N mm-2, 26.23-189.75 kJ at vertical loading position and 16.47-41.82 N, 1.68-11.08 mm, 0.34- 0.57 N mm-2, 27.67-319.99 kJ at horizontal loading position for Brown colored watermelon seed. The correlation between the mechanical properties and moisture content was statistically significant at (p≤0.05) level. It is also economical to load Black colored in vertical loading position at 27.8% moisture content and Brown colored in vertical loading position at 27.8% moisture content to reduce energy demand when necessary to crack or compress the seed. This research has generated data that are efficiently enough to design and fabricate processing and storage structures for Black and Brown water melon seeds.

PERANCANGAN ALAT UJI DEFLEKSI BATANG KANTILEVER FLEKSIBEL

Deflection is the change in shape experienced by the beam in the y direction due to the vertical loading applied to the beam or bar. Cantilever rods are if one end of the beam/rod is clamped and the other end is free. In this study, a flexible cantilever rod deflection test device was designed. This tool is used to determine the deflection/deflection that occurs in the beam/strip plate after being given a load. The method used is library research, a data collection method that is carried out by reading, studying, and researching the relevant literature with the title of this thesis which aims to collect data and analyze a theoretical understanding. This research will focus on designing and testing flexible cantilever rod deflection test equipment and utilizing beam/ strip plate as a test specimen for flexible cantilever rods. This tool has a height of 100 cm and a width of 90 cm and this tool is equipped with an HC-SR04 sensor which is directly connected to a digital number. The results of testing the strip plate with a load of 1 kg and 1.5 kg using the HC-SR04 sensor showed that the deflection at the smallest end was 20 mm, and the largest value was 30 mm. the theoretical calculation with equation (2-9) obtained the smallest result of 1.06 mm and the largest value of 3.5 mm.Defleksi adalah perubahan bentuk yang dialami balok pada arah y akibat adanya pembebanan vertikal yang diberikan terhadap balok atau batang. Batang kantilever yaitu jika salah satu ujung balok/batang dijepit dan yang ujung lain bebas. Pada penelitian ini dirancang sebuah alat uji defleksi batang kantilever fleksibel alat ini difungsikan untuk menentukan lendutan/defleksi yang terjadi pada beam/plat strip setelah diberi beban. Metode yang digunakan yaitu dengan penelitian kepustakaan suatu metode pengumpulan data yang dilakukan secara membaca, mempelajari, dan meneliti literature-literature yang relevan dengan judul skripsi ini yang bertujuan untuk mengumpulkan data dan menganalisa suatu pengertian yang bersifat teoritis. Pada penelitian ini akan berfokus pada perancangan dan uji coba alat uji defleksi batang kantilever fleksibel dan memanfaatkan beam/plat strip sebagai bahan spesimen uji batang kantilever fleksibel. Alat ini mempunyai tinggi 100 cm dan lebar 90 cm dan alat ini dilengkapi dengan sensor HC-SR04 yang langsung terhubung dengan digital number. Hasil pengujian plat strip beban 1 kg, dan 1.5 kg menggunakan sensor HC-SR04 didapatkan hasil defleksi pada ujung yang terkecil yaitu 20 mm, dan pada nilai yang terbesar 30 mm. pada perhitungan secara teoritis dengan persamaan (2-9) didapatkan hasil terkecil 1.06 mm dan nilai yang terbesar 3.5 mm.

Experimental Behavior of Precast Bridge Deck Systems with Non-Proprietary UHPC Transverse Field Joints

Full-depth precast bridge decks are widely used to expedite bridge construction and enhance durability. These deck systems face the challenge that their durability and performance are usually dictated by the effectiveness of their field joints and closure joint materials. Hence, commercial ultra-high performance concrete (UHPC) products have gained popularity for use in such joints because of their superior mechanical properties. However, the proprietary and relatively expensive nature of the robust UHPC mixes may pose some limitations on their future implementation. For these reasons, many research agencies along with state departments of transportation sought their way to develop cheaper non-proprietary UHPC (NP-UHPC) mixes using locally supplied materials. The objective of this study is to demonstrate the full-scale application of the recently developed NP-UHPC mixes at the ABC-UTC (accelerated bridge construction university transportation center) in transverse field joints of precast bridge decks. This study included experimental testing of three full-scale precast bridge deck subassemblies with transverse NP-UHPC field joints under static vertical loading. The test parameters included NP-UHPC mixes with different steel fibers amount, different joint splice details, and joint widths. The results of this study were compared with the results of a similar proprietary UHPC reference specimen. The structural behavior of the test specimens was evaluated in terms of the load versus deflection, reinforcement and concrete strains, and full assessment of the field joint performance. The study showed that the proposed NP-UHPC mixes and field joint details can be efficiently used in the transverse deck field joints with comparable behavior to the proprietary UHPC joints. The study concluded that the proposed systems remained elastic under the target design service and ultimate loads. In addition, the study showed that the use of reinforcement loop splices enhanced the load distribution across the specimen’s cross-section.

Investigating the Effect of Nonrigid Connectors on the Success of Tooth-and-Implant-Supported Fixed Partial Prostheses in Maxillary Anterior Region: A Finite Element Analysis (FEA)

Objective. This study was designed to assess the effect of nonrigid connectors (NRCs) and their location in the success of tooth-and-implant-supported fixed prostheses in the maxillary anterior region by finite element analysis (FEA). Materials and Methods. Three 3D FEA models were designed, presuming maxillary lateral incisor and canine to be extracted. Implant (replacing canine), abutment, bone (spongious and cortical), central incisor (containing dentin, root cement, gutta-percha, and casting post and core), periodontal ligament, and three three-unit cemented PFM prostheses (a rigid one and two nonrigid) were modeled. The NRC was once in the tooth side and once in the implant side. The prostheses were loaded twice: 250N to the incisal edges (0° to the long axis) and 200 N to the cingula (45° to the long axis). The von-Mises stress and vertical displacement were analyzed. Results. Under both vertical and oblique loadings, the rigid model presented the highest stress. Under vertical loading, the NRC caused a significant decrease in the applied stress to the prosthesis, bone, implant, and tooth. Locating the NRC in the tooth side decreased the applied stress to the prosthesis and NRC. Under oblique loading, prosthesis and implant tolerated less stress in the presence of an NRC. Placing the NRC in the tooth side resulted in the least stress in all of the components except for porcelain and patrix. Vertical displacement of the tooth apex was approximately equal in all models. Conclusion. Using an NRC on the tooth side is the most efficient method in reducing the applied stress to prosthesis, implant, tooth, and bone. The amount of intrusion is not dependent on using an NRC or not.

Analysis of Equivalent Flexural Stiffness of Steel–Concrete Composite Beams in Frame Structures

Vertical deflection of a frame beam is an important indicator in the limit-state analysis of frame structures, particularly for steel–concrete composite beams, which are usually designed with large spans and heavy loads. In this study, the equivalent flexural stiffness of composite frame beams is analysed to evaluate their vertical deflection. A theoretical beam model with a spring constraint boundary and varied stiffness segments is established to consider the influence of both the rotation restraint stiffness at the beam ends and the cracked section in the negative moment region, such that the inelastic bending deformation of the composite beams can be elaborately described. By an extensive parametric analysis, a fitting formula for evaluating the equivalent flexural stiffness of the composite beams, including the effects of the rotational constraint and the concrete cracking, is obtained. The validity of the proposed formula is demonstrated by comparing its calculation accuracy with those of existing design formulas for analysing the equivalent flexural stiffness of the composite beam members. Moreover, its utility is further verified by conducting non-linear finite element simulations of structural systems to examine the serviceability limit state and the entire process evolution of beam deflections under vertical loading. Finally, to facilitate the practical application of the proposed formula in engineering design, a simplified method to calculate the deflection of composite beams, which utilises the internal force distribution of elastic analysis, is presented based on the concept of equivalent flexural stiffness.