ANALYSES OF MULTI-EDGE FOOTINGS RESTED ON LOOSE AND DENSE SAND

Shallow footings are generally designed as square, rectangular, strip, circular or ring in geotechnical engineering. In some cases, different shallow footing geometries (irregular footing geometries) also can be selected because of the static, architectural and economical reasons. Multi-edge shallow footings are irregular shaped footings having the number of the edges and sides greater than four. They are used to transmit the loads from the irregular shaped structures to the underlying soils safely and economically. The study presented herein describes the use of artificial neural networks (ANNs) and multi-linear regression model (MLR) for prediction of ultimate loads of multi-edge shallow footings. The data used in running of network models have been obtained from extensive series of laboratory model tests. The parameters investigated are the footing width, the footing length and the density of sand soil. A total of fifty tests were performed using the parameters of the footing geometry (H, +, T and square shaped), the footing size and the soil type (loose sand, dense sand) on the bearing capacity characteristics. The results of the experimental study proved that the soil density and the footing size had considerable eects on the load of and the ANN model serves as simple and reliable tool for predicting the behavior of the multi-edge footings

Evaluation of Subgrade Modulus and Bearing Capacity with Large Scale Field Tests on Geogrid-Reinforced Granular Fill over Clay Soil

This study aims at experimentally explaining the potential benefits of geogrid reinforcedsoil foundations using large scale field tests. A total of 8 large scale field tests were carriedout to evaluate the effects of replacing natural clay soil with stronger granular fill layer andsingle-multiple layers of geogrid reinforcement placed into granular fill below circularfootings. The large scale field tests were performed using two different sizes of the circularfooting diameters which have 0.30 and 0.90m. The results of testing program are presented interms of subgrade modulus and bearing capacity. Subgrade modulus and bearing capacityvalues were calculated for each test at settlements of 10, 20 and 30mm.It has been seen that based on the test results, the use of granular fill and geogrid forreinforced soil foundations (RSF) have considerable effects on the subgrade modulus andbearing capacity

Prediction of bearing capacity of circular footings on soft clay stabilized with granular soil

AbstractThe shortage of available and suitable construction sites in city centres has led to the increased use of problematic areas, where the bearing capacity of the underlying deposits is very low. The reinforcement of these problematic soils with granular fill layers is one of the soil improvement techniques that are widely used. Problematic soil behaviour can be improved by totally or partially replacing the inadequate soils with layers of compacted granular fill. The study presented herein describes the use of artificial neural networks (ANNs), and the multi-linear regression model (MLR) to predict the bearing capacity of circular shallow footings supported by layers of compacted granular fill over natural clay soil. The data used in running the network models have been obtained from an extensive series of field tests, including large-scale footing diameters. The field tests were performed using seven different footing diameters, up to 0.90m, and three different granular fill layer thicknesses. The results indicate that the use of granular fill layers over natural clay soil has a considerable effect on the bearing capacity characteristics and that the ANN model serves as a simple and reliable tool for predicting the bearing capacity of circular footings in stabilized natural clay soil

The effect of thrombolytic therapy on QT dispersion in acute myocardial infarction and its role in the prediction of reperfusion arrhythmias

Purpose: We aimed to determine the effect of intravenous thrombolytic therapy on QT dispersion (QTd) and its role in the prediction of reperfusion arrhythmias.Materials and Methods: Twenty patients with acute myocardial infarction (MI) were enrolled in the study. Measurements of QTd were carried out  prior to thrombolytic therapy and before discharge. The patients were examined for ventricular arrhythmias with 24‑h Holter electrocardiography monitoring after treatment and the relationship between ventricular arrhythmias and the QTd values in the early phase of MI was investigated.Results: The values of QTd were significantly higher during the early phase of MI (60 ± 5.32 ms) than those in the late phase (53.35 ± 4.07 ms) (P = 0.032). There was no correlation between isolated, bigeminal, trigeminal and total ventricular premature beats, accelerated idioventricular rhythm (AIVR) with QTd values. However, the patients with sustained ventricular tachycardia (VT), prolonged VT and sustained AIVR had higher corrected QTd (92 ms1/2, 97.8 ms1/2, 81.7 ms1/2, respectively) than the patients without these arrhythmias (74 ms1/2, 56.3 ms1/2, 58.28 ms1/2,  respectively) (P = 0.022, 0.013, 0.018).Conclusion: The values of QTd may be significantly reduced in the 1st week of acute MI and measurement of QTd in the early phase of MI may have a correlation with the following reperfusion arrhythmias: Sustained VT, prolonged VT and AIVR.Key words: Arrhythmia, myocardial infarction, QT dispersion, reperfusion, thrombolytic therap

Microsurgical Clipping of Anterior Circle of Willis Aneurysms: A Retrospective Study

Objective: The surgical outcomes of anterior circle of Willis aneurysms were evaluated.Material and Methods: Between March 2015 and December 2016, 38 patients were operated and followed up for aneurysms. There were 15 female and 23 male patients with a mean age of 47 years (range: 17-78). Of the patients, 35 were diagnosed with subarachnoid hemorrhage (SAH). Of these patients, 54.2% (n=19) were operated within the first 24 hours. All patients were operated by the same surgeon with sylvian dissection. All clinical data in the hospital charts and outpatient records and radiological investigations stored in the archive were evaluated retrospectively.Results: The most commonly seen aneurysm was on the anterior communicating artery (44.8%). After that, aneurysms on the middle cerebral artery (31.6%), posterior communicating artery (13.2%), internal cerebral artery bifurcation (7.8%), and distal anterior cerebral artery were seen, respectively. There was a significant correlation between the location of the aneurysm and the mean age (p=0.009). All patients were followed in the intensive care unit after operation. After surgery, vasospasm was observed in 26.3% of patients. Patients with high SAH grade developed vasospasm significantly more frequently (p=0.03). Neurological examinations at discharge were normal in 17 patients with SAH and 3 patients without SAH. Four patients were discharged with minimal neurological deficit and 2 patients with severe deficit. Eight patients with World Federation of Neurosurgical Societies (WFNS) grade 4-5, 2 patients with grade 3, and 2 patients with grade 1-2 were lost. Postoperative Glasgow Coma Scale and SAH WFNS grades were found to be determinants for dying.Conclusion: Despite the development of endovascular techniques in the treatment of aneurysm, microsurgical clipping remains the first choice method to treat anterior system aneurysms. Closure of the aneurysm is the treatment priority. It is well known that early surgery reduces mortality and morbidity

Sudden Onset of Tetraparesis During Taking of Magnetic Resonance Imaging in a Patient with Undiagnosed Cervical Spinal Stenosis: A Case Report

Objective: To report a case with sudden-onset tetraparesis during taking magnetic resonance imaging (MRI).Case report: A 73-year-old man was referred with complaints of paresis of his arms and legs. His tetraparesis had developed suddenly while an MRI was performed 10 days before. He had a severe tetraparesis with 0/5 motor strength in his legs and 2/5 motor strength in his arms. On the MRI, a serious spinal stenosis at C3-4 and C4-5 levels and a faint myleopathic signal of the spinal cord at the level of the C4-5 disc space were seen. After posterior decompression, the patient’s tetraparesis improved gradually and he could walk independently and perform his daily activities with mild spasticity after 13 months.Conclusion: It is known that sudden neurological deficits may be seen in cervical trauma in patients with cervical spinal stenosis due to spondylosis. However, this case who did not have a trauma history showed us that a long period of positioning the neck beyond the patient’s control, even during the execution of MRI, may cause sudden deterioration

Eksperimentalne in numerične študije T-oblikovanih temeljev

In addition to vertical axial loads, the footings of structures are often subjected to eccentric loads caused by the forces of earth pressures, earthquakes, water, wind, etc. Due to eccentric loading, the two edges settle by different amounts, causing the footing to tilt and then the pressure below the footing does not remain uniform. The T-shape is proposed as a footing shape for improving the bearing capacity of shallow footings against the action of eccentric loads. The vertical insertion of the rigid T-shaped footing, into the bearing soil, provides considerable resistance, against both of sliding and overturning, enough to regain the reduction in bearing capacity and increase in settlement. In this study, a series of experimental and numerical results from the ultimate loads and settlement of T-shaped footings are reported. A total of 48 model tests were conducted for investigating the effects of different parameters, such as the problem geometry and soil density. The problem geometry was represented by two parameters, the load eccentricity (e) and the insertion depth (H) of the T-shape into the loose and dense sand soil. After the experimental stage, the numerical analyses were carried out using a plane strain, two-dimensional, finite-element-based computer program. The behaviour of the T-shape footing on sand beds is represented by the hardening soil model. The results of the experimental and numerical studies proved that the ultimate bearing capacity of a footing under eccentric loads could be improved by inserting a vertical central cut-off rigidly connected to the footing bottom. The load settlement curves indicate that the higher load eccentricity results in a decrease in the bearing capacity of the strip footing. It was also proved that the ultimate bearing capacity values can, depending on the soil density, be improved by up to four times that of the loose sand case. This investigation is considered to have provided a useful basis for further research, leading to an increased understanding of the T-shaped footing design.Temelji konstrukcij so podvrženi vertikalnim osnim obremenitvam, pogosto pa tudi ekscentričnim obremenitvam, ki jih povzročajo sile zemeljskega pritiska, potresov, vode, vetra itd. Zaradi ekscentričnih obremenitev se robova temelja posedata različno, kar povzroči nagibanje temelja in spremembo pritiska pod temeljem. Predlagana T-oblika temelja naj bi izboljšala nosilnost plitkih temeljev pri ekscentričnih obremenitvah. Pri vertikalni vstavitvi togih T-temeljev v nosilno zemljino pride do precejšnjega upora proti drsenju in prevrnjenju, ki je tako velik, da se nosilnost še zmanjša in posedanje poveča. V članku so predstavljeni številni eksperimentalni in numerični rezultati posedanja temeljev zaradi skrajnih obremenitev. Za preučevanje vplivov različnih parametrov, kot npr. problema geometrije in gostote zemljine, smo pripravili 48 modelnih preizkusov. Problem geometrije smo predstavili z dvema parametroma, ekscentričnostjo obremenitve (e) in globino vstavljanja (H) T-temelja v rahlo in gosto peščeno zemljino. Eksperimentalnemu delu so sledile še numerične analize, za katere smo uporabili računalniški program za ravninske deformacije z dvodimenzionalnimi končnimi elementi. Obnašanje T-temelja na peščenih posteljicah smo predstavili z modelom uterjevanja zemljine. Rezultati eksperimentalnih in numeričnih študij dokazujejo, da se lahko nosilnost temelja pri skrajnih ekscentričnih obremenitvah izboljša z vstavljanjem vertikalnega centralnega dela, ki se togo pritrdi na dno temelja. Krivulje posedanja zaradi obremenitve kažejo, da višja obremenitev privede do zmanjšanja nosilnosti pasovnega temelja. Dokazali so tudi, da se lahko glede na gostoto zemljine, v primerjavi z rahlim peskom, nosilnost temelja izboljša do štirikrat. Menimo, da je dala raziskava koristno osnovo za nadaljnje raziskovanje in omogočila boljše razumevanje T-temeljev

Stress Analyses of Strip and Rectangular Footings Rested on Loose Sands

In this study, the stress, the bearing capacity and the settlement behavior in the loose sandy soils were investigated experimentally and theoretically. The study was performed in central loading conditions using strip and rectangular footings. The vertical stresses resulting from the external are measured for three different distances simultaneously. And also the load-settlement curves were obtained. The results showed that the bearing capacity increases when the length of the footing increases and the measured vertical stress values decrease along the depths for all the three types of the footing types. The test results were compared with theoretical results given in the literature. As seen from this comparison, the experimental results are in accordance with the theoretical results

Numerična analiza okroglega temelja na naravni glini, stabilizirani z zrnatim polnilom

In this study, numerical predictions of the scale effect for circular footings supported by partially replaced, compacted, layers on natural clay deposits are presented. The scale- effect phenomenon was analyzed according to the footing sizes. Numerical analyses were carried out using an axisymmetric, two-dimensional, finite-element program. Before conducting the analysis, the validity of the constitutive model was validated using field tests performed by authors with seven different footing diameters up to 0.90 m and with three different partial replacement thicknesses. It is shown that the behavior of the circular footings on natural clay soil and the partial replacement system can be reasonably well represented by the Mohr Coulomb model. The Mohr-Coulomb model parameters were derived from the results of conventional laboratory and field tests. After achieving a good consistency between the results of the test and the numerical analysis, the numerical analyses were continued by increasing the footing diameter up to 25 m, considering the partial replacement thickness up to two times the footing diameter. The results of this parametric study showed that the stabilization had a considerable effect on the bearing capacity of the circular footings and for a given value of H/D the magnitude of the ultimate bearing capacity increases in a nonlinear manner with the footing diameter. The Bearing Capacity Ratio (BCR) was defined to evaluate the improved performance of the reinforced system. It was found, based on numerical and field-test results that the BCR of the partially replaced, natural clay deposits increased with an increase in the footing diameter and there was no significant scale effect of the circular footing resting on natural clay deposits.V tej študiji so predstavljene numerične napovedi obsega učinka na okrogle temelje, podprtih z delno zamenjanimi in zgoščenimi plastmi na usedlinah naravne gline. Pojav obsega učinka je analiziran glede na velikost temelja. Numerične analize so bile izvedene z uporabo osno simetričnega, dvodimenzionalnega programa s končnimi elementi. Pred izvedbo analize je bila potrjena veljavnost osnovnega modela z uporabo terenskih testov s sedmimi različnimi premeri temeljev do 0,90 m in s tremi različnimi delno zamenjanimi debelinami. Izkazalo se je, da lahko obnašanje okroglih temeljev na tleh iz naravne gline in delno zamenjanim sistemom dovolj primerno prikažemo z Mohr-Coulombovim modelom. Parametri Mohr Coulombovega modela so izpeljani iz rezultatov z običajnimi laboratorijskimi in s terenskimi testi. Z doseženo dobro složnostjo med rezultati testa in numeričnimi analizami, so bile nadaljevane numerične analize s povečevanjem premera temeljev do 25m in upoštevanjem z delno zamenjavo debeline do dvakratnega premera temeljev. Rezultati te parametrične študije so pokazale, da ima stabilizacija precejšen učinek na nosilno kapaciteto okroglih temeljev in da se pri dani vrednosti H/D magnituda mejne nosilne kapacitete poveča s premerom temelja na nelinearni način. Določen je količnik nosilne kapacitete (BCR) za določitev izboljšanega učinka ojačenega sistema. Na podlagi rezultatov numeričnih in terenskih testov je ugotovljeno, da se BCR delno zamenjanih odloženih naravnih glin poveča s povečanjem premera temeljev in da ni pomembnega obsega učinka okroglega temelja ležečega na usedlini z naravno glino