Identifying Effective and Ineffective Retrofits for Distortion Fatigue Cracking in Steel Bridges Using Field Instrumentation

It is estimated that nearly 90% of all fatigue cracking is the result of out-of-plane distortion or other unanticipated secondary stresses at fatigue-sensitive details. Neither design specifications nor evaluation specifications provide any guidance on how to evaluate the in-service potential for fatigue cracking at these details. Often, as a result, the effectiveness of various retrofit procedures is questionable and ill fated. There are many examples where implemented retrofit procedures did not work and fatigue cracking reinitiated or continued. Implementation of one or two prototype retrofits is an attractive alternative to ensuring effective retrofits are developed where many details have to be retrofitted. Field instrumentation and testing is an effective means to determine the effectiveness and behavior of a given retrofit strategy. Behavior that may not be anticipated can be identified prior to installing retrofits on a large scale, thereby preventing future problems. This paper provides guidance on how to instrument these details and examines one example where initial retrofit strategies did not work, as demonstrated by their performance through field instrumentation.     

多形态裂隙砂岩水力耦合破坏过程与增透机理试验研究

水力耦合激活岩石天然裂隙,诱导裂隙扩展形成复杂裂隙网络,增加岩石渗透性是矿产地热共采体系中的关键技术。本文通过预制含单裂隙、T型裂隙和Y型裂隙的砂岩试样,进行三轴水力耦合试验,研究多形态裂隙砂岩的关键阈值（闭合应力、起裂应力、损伤应力、峰值强度）、弹性模量、泊松比以及破坏模式等力学特性,同时开展裂隙渐进演化过程中声发射和渗透率的演化规律研究,进一步分析水力耦合作用下裂隙岩石增透机理。结果表明:多形态预制裂隙砂岩试样在水力耦合作用下,既有裂隙均通过拉伸、剪切或混合模式扩展形成次生裂纹,构成裂隙网络,试样渗透率显著增加。单裂隙试样的次生裂隙以剪切破坏为主,T型和Y型裂隙试样的次生裂隙为剪切破坏和张拉-剪切破坏两类。此外,多形态裂隙对试样强度的影响大于水的弱化作用。随着轴压增大,岩石渗透率峰前阶段先减小后增大,达到强度破坏时突跳增大。当试样达到峰值后应力突然下降时,渗透率达到最大值,渗透率增透效果最好。预制裂隙角度和形态的变化对突跳系数的影响幅度较小,单裂隙的平均突跳系数值大于Y型裂隙大于T型裂隙。研究结果有助于理解裂隙破坏和流体流动行为,进而指导矿产地热共采的工程。      

Fatigue Behavior and Retrofit Investigation of Distortion-Induced Web Gap Cracking

This paper studies a Kansas Department of Transportation welded plate girder bridge that developed fatigue cracks at small web gaps close to the girder top flange. Repair had been previously performed by softening the connection plate end with a slot retrofit, but cracks were recently found to have reinitiated at some of the repaired details and are again propagating. A comprehensive finite-element method study was performed to investigate the cracking behavior observed in the bridge and to recommend appropriate measures for future bridge retrofit. The analytical results show that stresses developed at the top flange web gaps could exceed yielding under the loading of an HS15 fatigue truck. The current slot repair used in the bridge was found to have introduced higher magnitude fatigue stresses in the web gap. To achieve a permanent repair of the bridge, it is recommended that a welded connection plate to flange attachment be used during future bridge retrofit. The web gap details should be able to withstand unlimited number of load cycles once this additional repair is performed.     

Modified laboratory culture techniques for the European cuttlefish Sepia officinalis

Stress fractures of the tarsal navicular bone are rare injury and assessing its healing is difficult. Tenderness over the tarsal navicular on physical examination is the most reliable sign for assessing fracture healing. However, it is desirable to assess fracture healing with some imaging method. We used serial magnetic resonance imaging (MRI) to assess healing in a patient with a tarsal navicular stress fracture. MRI was useful for the assessment of fracture healing of tarsal navicular stress fracture in our case.     

Investigation of Large Web Fractures of Welded Steel Plate Girder Bridge

Constructed in 1972 with ASTM A36 (250 MPa) steel, a highway bridge in Maryland is comprised of seven welded steel plate girders of a constant web depth of 2,286 mm (90 in.). In March 2003, the web fractures of two steel girders were discovered in a three-span continuous superstructure unit. A full-height web fracture occurred in an interior girder at a cross frame connection plate; and a partial-height web fracture occurred in an exterior girder at an intermediate transverse stiffener next to a cross frame. The investigation of the girder fractures involved fracture surface examination, material testing, fracture mechanics analysis, and comprehensive finite-element modeling for fracture driving forces. The fracture mechanics analysis indicated that a brittle web fracture could occur at a high stress level with either a surface crack or a through-thickness crack of certain dimensions. Finite-element analysis using a global model and submodels investigated three possible causes: (1) localized distortion of the unsupported web gap due to the lateral forces of cross frame members; (2) fabrication induced out-of-flatness of the web plate under in-plane loading; and (3) residual stresses at the fracture origin area due to the stiffener-to-web welds. The investigation concluded that one or a combination of these can result in the high local tensile stresses triggering a brittle web fracture with certain crack dimensions at the fracture origin area. Several retrofit concepts were investigated for their effectiveness in reducing stresses in the fracture origin area. Bridge inspections in the subsequent 6 years after the web fractures have not reported any other cracks in the bridge.     

Poor results following internal fixation of displaced subcapital femoral fractures: complacency in fracture reduction

The results following internal fixation of displaced subcapital femoral fractures are poorer than for undisplaced fractures and are determined by both the quality of the initial reduction and the accuracy of implant placement. In a series of 26 consecutive displaced fractures internally fixed with Richards hip pins, satisfactory reduction was achieved in only 15 hips. Accurate reduction is a prerequisite for correct screw placement and occurred in only 4 of the 11 poorly aligned fractures, as opposed to 11 of the 15 well reduced ones. A total of 10 hips required a further surgical procedure as the result of complications. These results highlight the importance of accurate fracture reduction in facilitating implant placement as well as the importance of good surgical technique rather than reliance purely upon the implant. These already common fractures are assuming increasing socioeconomic importance as the elderly population grows, and successful management is vital for both the individual patient and future demands on the health service.     

CFRP Composite Connector for Concrete Members

Steel plate connections are frequently used in tilt-up and precast concrete building construction to tie adjacent wall panels together for shear and overturning effects, and to provide continuous diaphragm chord connections for wind and seismic loading. These welded connectors perform poorly in regions of high seismicity and are vulnerable to corrosion. Until now, retrofit and repair strategies for in-plane shear transfer strengthening were limited to attaching steel sections across panel edges. In the present paper, an experimental program is described that utilizes carbon fiber reinforced plastic (CFRP) composites to develop a viable retrofit scheme for precast concrete shear walls and diaphragms. Nine full-scale precast wall panel assemblies with CFRP composite connectors have been tested. The results show that the CFRP composite connection is an effective solution for the seismic retrofit and repair of precast concrete wall assemblies and other precast concrete elements, such as horizontal diaphragms, that require in-plane shear transfer strengthening.     

Anorectal diseases

Fracture of the tibia is a well-known, often occult cause of limping and leg pain in young children. This fracture is typically a hairline, oblique fracture of the shaft of the tibia, and in some cases the fracture can be so subtle that bone scintigraphy or follow-up radiography may be required for its detection. In addition, a variety of other fractures that are less well known and just as difficult to detect can occur in the tibia and the foot in young children. These fractures include plastic bowing and buckle-type fractures, especially of the fibula; impaction, compression, or stress (fatigue) fractures of the tibia and fibula; and fractures of the metatarsal and tarsal bones. All of these fractures can be remarkably similar to the non-displaced spiral tibial fracture in their clinical appearance and should be included under the rubric of "toddler's fracture."     

考虑端部摩擦的中心直裂纹巴西圆盘断裂参数解析解

运用权函数法推导出考虑加载端摩擦的四种形式分布载荷加载下,中心直裂纹巴西圆盘试样在任意I/II复合型断裂模式下I、II型应力强度因子及T应力的解析解,并探究了端部摩擦及载荷分布角度对断裂参数的影响。研究结果表明:（1）当中心裂纹相对长度β较小时,纯I型、纯II型断裂的Y_I、Y_II及T*（分别是量纲为一的I型、II型应力强度因子及T应力）均随摩擦系数及载荷分布角度增大而减小;但是,当β较大时,摩擦系数增大可使纯I型Y_I增大,而载荷分布角度增大可使纯II型T*增大。（2）接触载荷分布形式为常数函数时,载荷分布角度对断裂参数的影响最显著,而四次函数下其对断裂参数的影响相对最小。（3）当β较小时,纯II型加载角度随载荷分布角度增大而减小;当β较大时,其随载荷分布角度增大而增大;摩擦系数增大可使纯II型加载角度增大。      

Management of late induced abortions in France

OBJECTIVE: To evaluate the clinical results of comminuted patella fracture fixation after an extensile surgical approach by using a tibial tuberosity osteotomy. DESIGN: Prospective, clinical. PATIENTS: Six knees with displaced comminuted patella fractures had stable internal fixation after an osteotomy of the tibial tubercle. All had immediate postoperative continuous knee motion and were followed for an average of thirty-one months (minimum of eighteen months). OUTCOME MEASURES: Time to clinical and radiographic union, Hospital for Special Surgery (HSS) Knee Scores and comparisons with literature cohort studies. RESULTS: Clinical union of the osteotomy occurred at an average of eight weeks (range 6 to 12 weeks) and of the patella fractures at an average of eleven weeks (range 8 to 21 weeks). There was no radiographic evidence of osteotomy displacement, fracture implant loosening, migration, or failure. All patients had clinical residua, which included loss of motion, thigh muscle atrophy, and barometric complaints. HSS Knee Scores averaged 75 points with four good, one fair, and one poor result. These results were comparable to those of previously published reports of ablative surgery for this type of fracture. CONCLUSION: Comminuted patella fractures are severe injuries that usually result in some lingering morbidity. Internal fixation preserves bone stock, which facilitates future reconstructive procedures. The described tibial tuberosity osteotomy, patella eversion technique of fracture exposure improved visualization and reduction of the articular surface. The osteotomy healed in all cases and did not adversely affect the clinical results.     

Thymulin stimulates prolactin and thyrotropin release in an age-related manner

Reduction in the biomechanical competence of the axial skeleton can result in challenging complications. Osteoporosis consists of a heterogeneous group of syndromes in which bone mass per unit volume is reduced in otherwise normal bone, which results in more fragile bone. The geriatric population has an increased risk for debilitating postural changes because of several factors. The two most apparent factors are involutional loss of functional muscle motor units and the greater prevalence of osteoporosis in this population. Obviously, the main objective of rehabilitation is to prevent fractures rather than to treat the complications. These complications can vary from "silent" compression fractures of vertebral bodies, to sacral insufficiency fractures, to "breath-taking" fractures of the spine or femoral neck. The exponential loss of bone at the postmenopausal stage is not accompanied by an incremental loss of muscle strength. The loss of muscle strength follows a more gradual course and is not affected significantly by a sudden hormonal decline, as is the case with bone loss. This muscle loss may contribute to osteoporosis-related skeletal disfigurations. In men and women, the combination of aging and reduction of physical activity can affect musculoskeletal health, and contribute to the development of bone fragility. The parallel decline in muscle mass and bone mass with age is more than a coincidence, and inactivity may explain some of the bone loss previously associated with aging per se. Kyphotic postural change is the most physically disfiguring and psychologically damaging effect of osteoporosis and can contribute to an increment in vertebral fractures and the risk of falling. Axial skeletal fractures, such as fracture of the sacral alae (sacral insufficiency fracture) and pubic rami, may not be found until radiographic changes are detected. Management of chronic pain should include not only improvement of muscle strength and posture but also, at times, reduction of weight bearing on the painful pelvis with insufficiency fractures. Axial skeletal health can be assisted with improvement of muscular supportive strength. Disproportionate weakness in the back extensor musculature relative to body weight or flexor strength considerably increases the risk of compressing porous vertebrae. A proper exercise program, especially osteogenic exercises, can improve musculoskeletal health in osteoporotic patients. Exercise not only improves musculoskeletal health but also can reduce the chronic pain syndrome and decrease depression. Application of a proper back support can decrease kyphotic posturing and can expedite the patient's return to ambulatory activities. Measures that can increase safety during ambulatory activities can reduce risk of falls and fractures. Managing the musculoskeletal challenges of osteoporosis goes hand in hand with managing the psychological aspects of the disease.     

Acute closed humeral shaft fractures treated with dynamic compression plate

BACKGROUND: To define the efficacy of dynamic compression plates (DCPs) for the treatment of closed humeral shaft fractures. METHODS: A total of 165 patients with closed humeral shaft fractures were studied retrospectively. There were 120 patients who underwent open reduction and internal fixation with DCPs and no bone grafting (BG). Forty-five patients received the same procedures with BG. The mean follow-up period was 93 months. RESULTS: In the DCP without BG group, the average blood loss was 350 ml, operation time was 105 minutes, hospital stay was 8.5 days and fracture union time was 13.5 weeks. In the DCP with BG group, the average blood loss was 525 ml, operation time was 115 minutes, hospital stay was 7.9 days and fracture union time was 9.2 weeks. CONCLUSIONS: In our experience, DCPs are effective for surgical fixation of humeral shaft fractures. Prophylactic BG is recommended for cases with more comminution.     

W—Ni—Fe合金电子探针显微分析

阐述了用电子探针做显微分析的特点，拟定出了Ｗ－Ｎｉ－Ｆｅ合金断口分析和显微组织分析的方法；在断口分析中，讨论了断口样品制备、合金缺陷的观察和合会断裂的主要形式等问题；在显微组织分析中，讨论了抛光磨片制备、胶结相成分的测定、（ＮｉＦｅ）６Ｗ６Ｃ碳化物相的测定和Ｗ晶粒度的测定等问题。     

Norian SRS cement augmentation in hip fracture treatment. Laboratory and initial clinical results

Bone quality, initial fracture displacement, severity of fracture comminution, accuracy of fracture reduction, and the placement of the internal fixation device are important factors that affect fixation stability. New high strength cements that are susceptible to remodeling and replacement for fracture fixation may lead to improved clinical outcome in the treatment of hip fractures. Norian SRS is an injectable, fast setting cement that cures in vivo to form an osteoconductive carbonated apatite of high compressive strength (55 MPa) with chemical and physical characteristics similar to the mineral phase of bone. It can be used as a space filling internal fixation device to facilitate the geometric reconstruction, load transfer, and healing of bone with defects and/or fractures in regions of cancellous bone. Furthermore, this cement can improve the mechanical holding strength of conventional fixation devices. Use of this material potentially could improve fracture stability, retain anatomy during fracture healing and improve hip function, thus achieving better clinical outcomes. In vivo animal studies have shown the material's biocompatibility, and cadaveric studies have shown the biomechanical advantage of its use in hip fractures. Initial clinical experience (in 52 femoral neck fractures and 39 intertrochanteric fractures) showed the potential clinical use of this innovative cement in the treatment of hip fractures.     

Inotropic effects of glyceryl trinitrate and spontaneous NO donors in the dog heart

Facial fractures may portend intracranial and skullbase injury and may lead to rapid compromise of the airway. Primary care physicians may provide emergency care for patients who have sustained facial trauma. After immediate resuscitation and stabilization, management of facial fractures requires knowledge of the anatomy, rapid treatment methods and identification of potential associated injuries for each type of facial fracture. Differentiation between the life-threatening aspects of these injuries and the less urgent, but more apparent, facial injuries will lessen the risk of complications such as bleeding, meningitis and asphyxia. Knowledge of the anatomy of the facial skeleton and of the potential injuries associated with each of the various types of facial fractures will facilitate effective management decisions. Consultation should be sought when functional features are involved or when the injury threatens to produce future cosmetic anomalies.     

Mixed mode I/III fracture toughness of 2034 aluminum alloys

A study of the mixed mode I and III fracture resistance of four 2034 aluminum alloys with varying manganese content is presented in this paper. The mixed mode fracture tests are carried out using modified compact tension specimens. As there is no standard test method for mixed mode fracture, special formulations of the J integral are used to characterize the mixed mode fracture resistance. The results indicate that the overall effect of mode III shear component is to lower the critical J-integral energy by enhancing the tendency for shear instability and early void formation. Manganese present in small amounts forms intermediate size dispersoids which increase the strength and work hardening ability without the loss of fracture toughness. In larger amounts manganese forms large particles which lower the fracture toughness significantly. These micromechanisms and those of mixed mode fracture are discussed.     

Conceptual Model for Prediction of FRP-Concrete Bond Strength under Moisture Cycles

Fiber-reinforced polymer (FRP) retrofit systems for concrete structural members such as beams, columns, slabs, and bridge decks have become increasingly popular as a result of extensive studies on short-term debonding behavior. Nevertheless, long-term performance and durability issues regarding debonding behavior in such strengthening systems still remain largely uncertain and unanswered. Because of its composite nature, the effectiveness of the strengthening system depends on the properties of the interfaces between the three constituent materials; namely, concrete, epoxy, and FRP. Certain factors, including those related to environmental exposures, can cause degradation of the interface properties during service life. This is particularly critical when predicting service life and planning maintenance of FRP-strengthened concrete structures. In this study, effect of moisture on an FRP-concrete bond system is characterized by means of the tri-layer fracture toughness, which can be obtained experimentally from peel and shear fracture tests. Fracture specimens were conditioned under various durations and numbers of wet-dry cycles at room temperature and 50°C. An irreversible weakening in bond strength was observed in fracture specimens under moisture cyclic condition. A conceptual model is developed based on the experimental results of the fracture specimens under variable cyclic moisture conditions for the bond strength prediction of the FRP-concrete bond system. A numerical study of a precracked FRP-strengthened reinforced concrete beam is then performed to show potential application of the proposed predictive model.