Ahmed M. Farahat

Punching shear strength of reinforced concrete flat slabs subjected to fire on their tension sides

Abstract The effect of fire on punching strength of flat slabs is experimentally investigated. An experimental program, consisting of fourteen one-third scale specimens pre-exposed to fire on their tension side and tested under concentric punching, is carried out. The main investigated parameters are the duration of exposure to fire, the concrete cover and the cooling method. Specimens are subjected to direct flame for 1.0, 2.0 and 3.0 h, respectively. Concrete covers of 25 mm and 10 mm are used for test specimens. Two cooling methods are employed; gradual cooling in air and sudden cooling with water applied directly to the heated surface of the slabs. It was found that exposure of slabs to fire resulted in a reduction of up to 18.3% and 43% in cracking loads and ultimate punching loads, respectively. Concrete cover was proven to have a significant effect on level of temperature in tension reinforcement. A reduction in punching strength of up to 14% was observed for specimens with 3 h exposure to fire compared to those with one hour exposure. Sudden cooling was found to reduce punching strength by 25% compared to specimens gradually cooled. A simplified mechanical model for calculating fire effect on punching capacity is proposed and found to be in good agreement with the experimental results.

Strain-space plasticity model for the compressive hardening-softening behaviour of concrete

Abstract Concrete exhibits strong strain-softening behaviour in the post-failure range. To simulate the strains-oftening behaviour in concrete structures, numerous stress-space plasticity models have been proposed. Unfortunately, it is found that the application of the stress-space formulation of plasticity to concrete encounters difficulties in modelling the softening behaviour since it cannot explicitly give a clear distinction of loading, unloading and neutral loading. Strain-space formulation is therefore rational for further progress. Although several strain-space plasticity models are proposed, these models can simulate the strain-softening behaviour of concrete only under low confining pressure and they lack experimental verification since the available test data with softening behaviour are very limited. In this paper, a general form of strain-space plasticity formulations applied to strain-hardening-softening materials under both low and high confining pressure is developed. The strain-space formulation is presented by introducing the loading function as well as the plastic potential function, corresponding to those of Drucker-Prager type in the stress space. Two material parameters of the failure surface are determined from the test data on the compressive meridian. Experimental work is carried out to determine the model parameters. The model simulation is performed not only for the current experimental data but also for most of the available test data to demonstrate the capability of the model. It is found that the model can sufficiently predict the hardening as well as the softening behaviour of concrete under both low and high confining pressure.

Laparoscopy with laparoscopic ultrasound for pretreatment staging of hepatic focal lesions: a prospective study.

INTRODUCTION The need for accurate intrahepatic staging is crucial for patients with primary or secondary hepatic malignancies. Currently available data indicate that laparoscopy with laparoscopic ultrasound provides information similar to that obtained by intraoperative ultrasound and that it is able to identify small intrahepatic lesions not diagnosed by preoperative conventional imaging techniques. OBJECTIVE To determine the role of preoperative laparoscopy and laparoscopic ultrasonography in patients with potentially resectable hepatic focal lesion or candidate for radiofrequency ablation based on preoperative imaging. MATERIAL AND METHODS From March 2004 to March 2007, 55 patients with potentially resectable hepatic focal lesions were candidates for exploratory laparotomy based on preoperative abdominal ultrasonography and triphasic spiral CT. All cases were then reevaluated prior to surgery using laparoscopy and laparoscopic ultrasound. All these procedures were performed within a time period of no more than 4 weeks. The data obtained were compared to those obtained by the preoperative conventional imaging studies as regards the presence of satellites, subcentimetric lesions, newly discovered deep parynchymatous lesions, liver condition, portal vein thrombosis, nodal metastases, ascites, peritoneal implants, size and site of the primary lesion. RESULTS After performing ultrasound-guided laparoscopy, fourteen patients proved to be unfit for surgical resection or ablation, seven patients showed newly discovered focal lesions, five patients proved to have satellites around the tumor and peritoneal deposits, one patient had ascites and one patient had been falsely diagnosed as HCC, proved to have had a liver abscess. CONCLUSION Preoperative laparoscopy and laparoscopic ultrasonography as an adjunct to preoperative imaging techniques provide more accurate staging for patients with potentially resectable hepatic focal lesions.

Behavior of hybrid high-strength fiber reinforced concrete slab-column connections under the effect of high temperature

Abstract Concrete can be modified to perform in a more ductile form by the addition of randomly distributed discrete fibers in the concrete matrix. The combined effect of the addition of two types of fibers (steel fiber and polypropylene fiber with different percentages) to concrete matrix, which is called hybrid effect is currently under investigation worldwide. The current research work presents the conducted experimental program to observe the behavior of hybrid high strength reinforced concrete slab-column connections under the effect of high temperature. For this purpose, ten slab-column connections were casted and tested. The experimental program was designed to investigate the effect of different variables such as concrete mixture, column location and temperature fighting system. All specimens were exposed to a temperature of 500 °C for duration of two hours. To observe the effect of each variable, specimens were divided into four groups according to the studied parameters. The test results revealed that using hybrid high strength concrete HFHSC produced more strength in punching failure compared with high strength concrete HSC when exposed to elevated temperature. Fighting by air had higher initial crack load compared with that for without fighting and fighting by water. On the other hand, fighting by water decreased the ultimate load.

Skin sparing mastectomy: Technique and suggested methods of reconstruction

AIM To demonstrate the feasibility and accessibility of performing adequate mastectomy to extirpate the breast tissue, along with en-block formal axillary dissection performed from within the same incision. We also compared different methods of immediate breast reconstruction used to fill the skin envelope to achieve the best aesthetic results. METHODS 38 patients with breast cancer underwent skin-sparing mastectomy with formal axillary clearance, through a circum-areolar incision. Immediate breast reconstruction was performed using different techniques to fill in the skin envelope. Two reconstruction groups were assigned; group 1: Autologus tissue transfer only (n=24), and group 2: implant augmentation (n=14). AUTOLOGUS TISSUE TRANSFER The techniques used included filling in the skin envelope using Extended Latissimus Dorsi flap (18 patients) and Pedicled TRAM flap (6 patients). AUGMENTATION WITH IMPLANTS Subpectoral implants(4 patients), a rounded implant placed under the pectoralis major muscle to augment an LD reconstructed breast. LD pocket (10 patients), an anatomical implant placed over the pectoralis major muscle within a pocket created by the LD flap. No contra-lateral procedure was performed in any of the cases to achieve symmetry. RESULTS All cases underwent adequate excision of the breast tissue along with en-block complete axillary clearance (when indicated), without the need for an additional axillary incision. Eighteen patients underwent reconstruction using extended LD flaps only, six had TRAM flaps, four had augmentation using implants placed below the pectoralis muscle along with LD flaps, and ten had implants placed within the LD pocket. Breast shape, volume and contour were successfully restored in all patients. Adequate degree of ptosis was achieved, to ensure maximal symmetry. CONCLUSIONS Skin Sparing mastectomy through a circum-areolar incision has proven to be a safe and feasible option for the management of breast cancer in Egyptian women, offering them adequate oncologic control and optimum cosmetic outcome through preservation of the skin envelope of the breast when ever indicated. Our patients can benefit from safe surgery and have good cosmetic outcomeby applying different reconstructive techniques.

Detection of bacteria in the nasopharyngeal secretion and effusion associated with serous otitis media

Objective This study aimed at evaluating the accuracy of nasopharyngeal (NP) specimens in the identification of pathogens in the middle-ear fluid (MEF) in patients with otitis media with effusion. Materials and methods This was a prospective, hospital-based study with a cross-sectional design to evaluate the accuracy of NP isolates in identifying MEF pathogens and a case-control design to study NP secretion specimens taken from children undergoing an operation with no otologic indication, the middle-ear swab taken from patients undergoing stapedectomy, and middle-ear secretions taken from patients with secretory otitis media (SOM) of an older age group regarding the tympanogram result, radiograph, and endoscopy. Results The numbers and percentages of patients showed significant numbers of bacteria in both the MEF and the NP swap, and showed a statistically significant difference (P < 0.05). Conclusion Otitis media is the second most common disease of childhood and is responsible for a significant number of visits to the pediatrician. About 10% of the cases with middle-ear effusion after an episode of acute otitis media can persist for more than 3 months. Hearing loss associated with serous otitis media (SOM) can potentially have a detrimental effect on speech and language development.