Investigation of High Density Polyethylene Pipe for Highway Applications, HR-373, Phase 1, 1996

In the past, culvert pipes were made only of corrugated metal or reinforced concrete. In recent years, several manufacturers have made pipe of lightweight plastic - for example, high density polyethylene (HDPE) - which is considered to be viscoelastic in its structural behavior. It appears that there are several highway applications in which HDPE pipe would be an economically favorable alternative. However, the newness of plastic pipe requires the evaluation of its performance, integrity, and durability; A review of the Iowa Department of Transportation Standard Specifications for Highway and Bridge Construction reveals limited information on the use of plastic pipe for state projects. The objective of this study was to review and evaluate the use of HDPE pipe in roadway applications. Structural performance, soil-structure interaction, and the sensitivity of the pipe to installation was investigated. Comprehensive computerized literature searches were undertaken to define the state-of-the-art in the design and use of HDPE pipe in highway applications. A questionnaire was developed and sent to all Iowa county engineers to learn of their use of HDPE pipe. Responses indicated that the majority of county engineers were aware of the product but were not confident in its ability to perform as well as conventional materials. Counties currently using HDPE pipe in general only use it in driveway crossings. Originally, we intended to survey states as to their usage of HDPE pipe. However, a few weeks after initiation of the project, it was learned that the Tennessee DOT was in the process of making a similar survey of state DOT's. Results of the Tennessee survey of states have been obtained and included in this report. In an effort to develop more confidence in the pipe's performance parameters, this research included laboratory tests to determine the ring and flexural stiffness of HDPE pipe provided by various manufacturers. Parallel plate tests verified all specimens were in compliance with ASTM specifications. Flexural testing revealed that pipe profile had a significant effect on the longitudinal stiffness and that strength could not be accurately predicted on the basis of diameter alone. Realizing that the soil around a buried HDPE pipe contributes to the pipe stiffness, the research team completed a limited series of tests on buried 3 ft-diameter HDPE pipe. The tests simulated the effects of truck wheel loads above the pipe and were conducted with two feet of cover. These tests indicated that the type and quality of backfill significantly influences the performance of HDPE pipe. The tests revealed that the soil envelope does significantly affect the performance of HDPE pipe in situ, and after a certain point, no additional strength is realized by increasing the quality of the backfill.

Heavy Agricultural Loads on Pavements and Bridges, HR-1073, 1999

During the harvest season in Iowa, it is common to have single axle loads on secondary roads and bridges that are excessive (typical examples are grain carts) and well beyond normal load limits. Even though these excessive loads occur only during a short time of the year, they may do significant damage to pavements and bridges. In addition, the safety of some bridges may be compromised because of the excessive loads, and sometimes there may be little indication to the users that damage may be imminent. At this time there are no Iowa laws regulating axle loads allowed for agricultural equipment. This study looks at the potential problems this may cause on secondary roads and timber stringer bridges. Both highway pavement and timber bridges are evaluated in this report. A section (panel) of Iowa PCC paved county road was chosen to study the effects of heavy agricultural loads on pavements. Instrumentation was applied to the panel and a heavily loaded grain cart was rolled across. The collected data were analyzed for any indication of excessive stresses of the concrete. The second study, concerning excessive loads on timber stringer bridges, was conducted in the laboratory. Four bridge sections were constructed and tested. Two of the sections contained five stringers and two sections had three stringers. Timber for the bridges came from a dismantled bridge, and deck panels were cut from new stock. All timber was treated with creosote. A hydraulic load was applied at the deck mid-span using a foot print representing a tire from a typical grain cart. Force was applied until failure of the system resulted. The collected data were evaluated to provide indications of load distribution and for comparison with expected wheel loads for a typical heavily loaded single axle grain cart. Results of the pavement tests showed that the potential of over-stressing the pavement is a possibility. Even though most of the tension stress levels recorded were below the rupture strength of the concrete, there were a few instances where the indicated tension stress level exceeded the concrete rupture strength. Results of the bridge tests showed that when the static ultimate load capacity of the timber stringer bridge sections was reached, there was sudden loss of capacity. Prior to reaching this ultimate capacity, the load sharing between the stringers was very uniform. The failure was characterized by loss of flexural capacity of the stringers. In all tests, the ultimate test load exceeded the wheel load that would be applied by an 875 bushel single axle grain cart.

Strength Development of Concrete Based on Maturity and Pulse Velocity, MLR-95-03, 1995

The effect of curing temperature, in the range of 4.4 to 22.8 degrees C (40 to 73 degrees F), on strength development was studied based on the maturity and pulse velocity measurements in this report. The strength-maturity relationships for various mixes using a Type I cement and using a Type IP cement, respectively, were experimentally developed. The similar curves for early age strength development of both the patching concrete, using a Type I cement with the addition of calcium chloride, and the fast track concrete, using a Type III cement and fly ash, have also been proposed. For the temperature ranges studied, the strength development of concrete can be determined using a pulse velocity measurement, but only for early ages up to 24 hours. These obtained relationships can be used to determine when a pavement can be opened to traffic. The amount of fly ash substitution, up to 30%, did not have a significant influence on the strength-maturity relationship.

Double incretin receptor knock-out (DIRKO) mice present with alterations of trabecular and cortical micromorphology and bone strength.

A role for gut hormone in bone physiology has been suspected. We evidenced alterations of microstructural morphology (trabecular and cortical) and bone strength (both at the whole-bone - and tissue-level) in double incretin receptor knock-out (DIRKO) mice as compared to wild-type littermates. These results support a role for gut hormones in bone physiology. INTRODUCTION: The two incretins, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), have been shown to control bone remodeling and strength. However, lessons from single incretin receptor knock-out mice highlighted a compensatory mechanism induced by elevated sensitivity to the other gut hormone. As such, it is unclear whether the bone alterations observed in GIP or GLP-1 receptor deficient animals resulted from the lack of a functional gut hormone receptor, or by higher sensitivity for the other gut hormone. The aims of the present study were to investigate the bone microstructural morphology, as well as bone tissue properties, in double incretin receptor knock-out (DIRKO) mice. METHODS: Twenty-six-week-old DIRKO mice were age- and sex-matched with wild-type (WT) littermates. Bone microstructural morphology was assessed at the femur by microCT and quantitative X-ray imaging, while tissue properties were investigated by quantitative backscattered electron imaging and Fourier-transformed infrared microscopy. Bone mechanical response was assessed at the whole-bone- and tissue-level by 3-point bending and nanoindentation, respectively. RESULTS: As compared to WT animals, DIRKO mice presented significant augmentations in trabecular bone mass and trabecular number whereas bone outer diameter, cortical thickness, and cortical area were reduced. At the whole-bone-level, yield stress, ultimate stress, and post-yield work to fracture were significantly reduced in DIRKO animals. At the tissue-level, only collagen maturity was reduced by 9 % in DIRKO mice leading to reductions in maximum load, hardness, and dissipated energy. CONCLUSIONS: This study demonstrated the critical role of gut hormones in controlling bone microstructural morphology and tissue properties.

Volitional assessment of respiratory muscle strength.

Respiratory muscle weakness may induce dyspnoea, secretion retention and respiratory failure. Assessing respiratory muscle strength is mandatory in neuromuscular diseases and in case of unexplained dyspnoea. A step by step approach is recommended, starting with simple volitional tests. Using spirometry, respiratory muscle weakness may be suspected on the basis of an abnormal flow-volume loop or a fall of supine vital capacity. When normal, maximal inspiratory and expiratory pressures against a near complete occlusion exclude significant muscle weakness, but low values are more difficult to interpret. Sniff nasal inspiratory pressure is a useful alternative because it is easy and it eliminates the problem of air leaks around the mouthpiece in patients with neuromuscular disorders. The strength available for coughing is easily assessed by measuring peak cough flow. In most cases, these simple non invasive tests are sufficient to confirm or to eliminate significant respiratory muscle weakness and help the timely introduction of ventilatory support or assisted cough techniques. In a minority of patients, a more complete evaluation is necessary using non volitional tests like cervical magnetic stimulation of phrenic nerves.

Investigation of High-Strength Bolt-Tightening Verification Techniques, RB07-014

The current means and methods of verifying that high-strength bolts have been properly tightened are very laborious and time consuming. In some cases, the techniques require special equipment and, in other cases, the verification itself may be somewhat subjective. While some commercially available verification techniques do exist, these options still have some limitations and might be considered costly options. The main objectives of this project were to explore high-strength bolt-tightening and verification techniques and to investigate the feasibility of developing and implementing new alternatives. A literature search and a survey of state departments of transportation (DOTs) were conducted to collect information on various bolt-tightening techniques such that an understanding of available and under-development techniques could be obtained. During the literature review, the requirements for materials, inspection, and installation methods outlined in the Research Council on Structural Connections specification were also reviewed and summarized. To guide the search for finding new alternatives and technology development, a working group meeting was held at the Iowa State University Institute for Transportation October 12, 2015. During the meeting, topics central to the research were discussed with Iowa DOT engineers and other professionals who have relevant experiences.

Recovery of rotators strength after latarjet surgery.

The purposes of this study were to prospectively determine changes in rotator cuff strength before and after surgical shoulder stabilization by Bristow-Latarjet procedure and to better estimate time needed for rotator cuff strength recovery. 20 patients with recurrent anterior posttraumatic shoulder dislocation underwent internal (IR) and external (ER) rotator isokinetic evaluation before and 3, 6 and 21 months after Bristow-Latarjet surgery. In a seated position with 45° of shoulder abduction in the scapular plane, both shoulders were evaluated concentrically with a Con-Trex® isokinetic dynamometer at 180°∙s - 1, 120°∙s - 1 and 60°∙s - 1. 3 months post-surgery, IR and ER strength of the operated shoulder were significantly lower than before surgery ( - 28±20% for IR, - 17±17% for ER) (P<0.05). At 6 and 21 months post-surgery, IR and ER strength were comparable to strength before surgery; strength recovery is seen at 6 months post-surgery with long-term maintenance at 21 months. Given the weakness 3 months post-surgery, return to sports (including overhead and contact sports) should be discussed, and 6 months post-surgery may be a better point for an athlete to resume practicing sports. Isokinetic rotator cuff strength evaluation appears to be relevant in helping to determine the need of continuing strength rehabilitation. Pre-surgical evaluation contributes to the relevance of later comparisons.

Fast Track and Fast Track II - Cedar Rapids, Iowa, HR-544, Construction Report, 1989

Two lanes of a major four lane arterial street needed to be reconstructed in Cedar Rapids, Iowa. The traffic volumes and difficulty of detouring the traffic necessitated closure for construction be held to an absolute minimum. Closure of the intersections, even for one day, was not politically feasible. Therefore, Fast Track and Fast Track II was specified for the project. Fast Track concrete paving has been used successfully in Iowa since 1986. The mainline portion of the project was specified to be Fast Track and achieved the opening strength of 400 psi in less than twelve hours. The intersections were allowed to be closed between 6 PM and 6 AM. This could occur twice - once to remove the old pavement and place the base and temporary surface and the second time to pave and cure the new concrete. The contractor was able to meet these restrictions. The Fast Track II used in the intersections achieved the opening strength of 350 psi in six to seven hours. Two test sections were selected in the mainline Fast Track and two intersections were chosen to test the Fast Tract II. Both flexural and compression specimens were tested. Pulse velocity tests were conducted on the pavement and test specimens. Maturity curves were developed through monitoring of the temperatures. Correlations were performed between the maturity and pulse velocity and the flexural strengths. The project was successful in establishing the feasibility of construction at night, with no disruption of traffic in the daytime, using fast Track II. Both the Fast Track II pavements were performing well four years after construction.

A matter of time: delayed mate encounter postpones mating window initiation and reduces the strength of female choosiness

Reproductive success is determined by the presence and timing of encounter of mates. The latter depends on species-specific reproductive characteristics (e.g. initiation/duration of the mating window), season, and reproductive strategies (e.g. intensity of choosiness) that may potentially mitigate constraints imposed by mating windows. Despite their potentially crucial role for fitness and population dynamics, limited evidence exists about mating window initiation, duration and reproductive strategies. Here, we experimentally tested the mechanisms of initiation and the duration of the common lizard's Zootoca vivipara mating window, by manipulating the timing of mate encounter and analyzing its effect on (re-)mating probability. We furthermore tested treatment effects on female reproductive strategies, by measuring female choosiness. The timing of mate encounter and season did not significantly affect mating probability. However, a longer delay until mate encounter reduced female choosiness. Re-mating probability decreased with re-mating delay and was independent of mating delay. This indicates that mating window initiation depends on mate encounter, that its duration is fixed, and that plastic reproductive strategies exist. These findings contrast with previous beliefs and shows that mating windows per se may not necessarily constrain reproductive success, which is congruent with rapid range expansion and absence of positive density-effects on reproductive success (Allee effects). In summary, our results show that predicting the effect of mating windows on reproduction is complex and that experimental evidence is essential for evaluating their effect on reproduction and reproductive strategies, both being important determinants of population dynamics and the colonization of new habitats.

Statistical variation of weld profiles and their expected influence on fatigue strength

The general objective of this study was to conduct astatistical analysis on the variation of the weld profiles and their influence on the fatigue strength of the joint. Weld quality with respect to its fatigue strength is of importance which is the main concept behind this thesis. The intention of this study was to establish the influence of weld geometric parameters on the weld quality and fatigue strength. The effect of local geometrical variations of non-load carrying cruciform fillet welded joint under tensile loading wasstudied in this thesis work. Linear Elastic Fracture Mechanics was used to calculate fatigue strength of the cruciform fillet welded joints in as-welded condition and under cyclic tensile loading, for a range of weld geometries. With extreme value statistical analysis and LEFM, an attempt was made to relate the variation of the cruciform weld profiles such as weld angle and weld toe radius to respective FAT classes.

Prediction of soil shear strength in agricultural and natural environments of the Brazilian Cerrado

The objective of this work was to develop uni- and multivariate models to predict maximum soil shear strength (τmax) under different normal stresses (σn), water contents (U), and soil managements. The study was carried out in a Rhodic Haplustox under Cerrado (control area) and under no-tillage and conventional tillage systems. Undisturbed soil samples were taken in the 0.00-0.05 m layer and subjected to increasing U and σn, in shear strength tests. The uni- and multivariate models - respectively τmax=10(a+bU) and τmax=10(a+bU+cσn) - were significant in all three soil management systems evaluated and they satisfactorily explain the relationship between U, σn, and τmax. The soil under Cerrado has the highest shear strength (τ) estimated with the univariate model, regardless of the soil water content, whereas the soil under conventional tillage shows the highest values with the multivariate model, which were associated to the lowest water contents at the soil consistency limits in this management system.

The influence ofvariable amplitude loading on the fatigue strength of rhs corners

Rectangular hollow section (RHS) members are components widely used in engineering applications because of their good-looking, good properties in engineering areas and inexpensive cost comparing to members with other sections. The increasing use of RHS in load bearing structures makes it necessary to analyze the fatigue behavior of the RHS members. In this thesis, concentration will be given to the fatigue behavior of the RHS members under variable amplitude pure torsional loading. For the RHS members, failure will normally occur in the corner region if the welded regions are under full penetration. This is because of the complicated stress components' distributions at the RHScorners, where all of three fracture mechanics modes will happen. Mode I is mainly caused by the residual stresses that caused by the manufacturing process. Modes II and III are caused by the applied torsional loading. Stress based Findleymodel is also used to analyze the stress components. Constant amplitude fatigue tests have been done as well as variable amplitude fatigue tests. The specimens under variable amplitude loading gave longer fatigue lives than those under constant amplitude loading. Results from tests show an S-N curvewith slope around 5.

Constant and variable amplitude fatigue strength of high strength steel welds treated with ultrasonic impact treatment

Hitsattujen rakenteiden väsymiskestävyyttä pystytään parantamaan jälkikäsittelymenetelmillä, joistayksi, ultraäänikäsittely muokkaa hitsin geometriaa ja aiheuttaa puristusjäännösjännitystilan. Tässä tutkimuksessa verrataan kokeellisesti kuormaa kantamattoman hitsatun ja ui -käsitellyn rivan väsymislujuutta toisiinsa. Tutkimusohjelmaan kuuluu kahta teräslajia ja sekä vakio - että vaihtuva - amplitudista kuormitusta. Ultraäänikäsittelyllä saavutetaan väsymiskestoiän parantuminen vakio - ja vaihtuva - amplitudisella kuormituksella. Perusaineen lujuudella ei ole merkittää vaikutusta väsymislujuuteen kun liitos on hitsatussa tilassa. Tällöin väsymiskestävyyden määrää hitsin rajaviivan jännityskeskittymä. Ultraäänikäsitellyn hitsatunliitoksen väsymiskestävyys on suurempi korkeamman lujuuden omaavilla teräksillä. Tästä syystä korkealujuuksisten terästen käyttö ultraäänikäsiteltynä väsyttävästi kuormitetuissa kevytrakenteissa on perusteltua.

Effect of water contamination on the shear bond strength of five orthodontic adhesives

Objectives: To evaluate the shear bond strength and site of failure of brackets bonded to dry and wet enamel. Study design: 50 teeth were divided into ten groups of 5 teeth each (10 surfaces). In half the groups enamel was kept dry before bonding, and in the other half distilled water was applied to wet the surface after etching. The following groups were established: 1)Acid/Transbond-XT (dry/wet) XT; 2) Transbond Plus Self Etching Primer (TSEP)/Transbond-XT paste (dry/wet); 3) Concise (dry), Transbond MIP/Concise (wet), 4) FujiOrtho-LC (dry/wet); 5) SmartBond (dry/wet). Brackets were bonded to both buccal and lingual surfaces. Specimens were stored in distilled water (24 hours at 37ºC) and thermocycled. Brackets were debonded using a Universal testing machine (cross-head speed 1 mm/min). Failure sites were classified using a stereomicroscope. Results: No significant differences in bond strength were detected between the adhesives under wet and dry conditions except for Smart- Bond, whose bond strength was significantly lower under dry conditions. For all the adhesives most bond failures were of mixed site location except for Smartbond, which failed at the adhesive-bracket interface. Conclusions: Under wet conditions the bonding capacity of the adhesives tested was similar than under dry conditions, with the exception of SmartBond which improved under wet conditions