فهرست مطالب

پژوهشنامه حمل و نقل - سال پنجم شماره 4 (زمستان 1387)
  • سال پنجم شماره 4 (زمستان 1387)
  • تاریخ انتشار: 1387/10/11
  • تعداد عناوین: 7
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  • پریسا بازدار اردبیلی، عبدالرضا رضایی ارجرودی صفحه 295
    سرمایه گذاری در بخش حمل ونقل به منظور ایجاد اشتغال، در تجزیه و تحلیل مسائل اقتصاد کلان و سیاستگذاری از اهمیت فراوانی برخوردار است. به خصوص این امر در کشور ما تداعی کننده این امر است که از دیدگاه سیاستگذاران اقتصادی، عامل سرمایه به عنوان مکمل نیروی کار در بخش مربوطه به شمار می رود.
    در این مقاله، نقش سرمایه گذاری بر ایجاد اشتغال در بخش حمل ونقل در قالب رهیافت پویای تقاضای نیروی کار و بر اساس همگرایی، برآورد وتجزیه و تحلیل شده است. برای برآورد مدل، با استفاده از آمارهای موجود طی سال های 83-1350، ابتدا مرتبه جمعی بودن متغیرهای الگو و سپس ساختار الگو و تعداد وقفه های بهینه، مشخص می شود. در گام بعدی، تعداد بردارهای هم انباشتگی الگو تعیین شده و در نهایت، ارتباط سرمایه گذاری با تقاضای نیروی کار در بخش حمل ونقل مورد برآورد تجربی قرار می گیرد. به منظور ایجاد ارتباط بین روابط تعادلی بلندمدت میان متغیرها با نوسانات کوتاه مدت، الگوی تصحیح خطای برداری مربوط به روابط تعادلی برای متغیر اشتغال، در بخش حمل ونقل برآورد می شود.
    کلیدواژگان: سرمایه گذاری، اشتغال، رهیافت پویای تقاضای نیروی کار، مدل خود توضیح برداری(VAR)، مدل تصحیح خطای برداری (VECM)
  • یوسف ربانی، محمد مهدی سپهری، سیدحسام الدین ذگردی صفحه 307
    ایران دارای بنادر فراوان در خلیج فارس و دریای عمان است که بسیاری از آنها به دلایل گوناگون قادر به پذیرش کشتی های بزرگ نیستند. ایده استفاده از بنادر بزرگ موجود در منطقه به عنوان مراکز واسط برای دریافت کالا از کشتی های بزرگ و ارسال آن توسط کشتی های کوچک تر به سایر بنادر و از آنجا به داخل کشور می تواند در جهت فعال کردن بنادر کوچک تر و نیز کشتیرانی خصوصی در منطقه بسیار کارآمد باشد. در این مقاله علاوه بر طرح این ایده، یک سیستم کلی حمل ونقل متناسب با آن طرح شده و به صورت یک شبکه متشکل از مسیر های وسایل نقلیه و مسیر های حمل ونقل چند وجهی برای اولین بار مدل شده است. در این مقاله برای حل مدل این شبکه، برای مسائل با ابعاد کوچک، از روش انشعاب و تحدید استفاده شده و برای حل مدل های دارای تعداد گره بیشتر، روشی ابتکاری به نام SB RAB بر اساس روش سیمپلکس با ورود محدود متغیرها توسعه داده شده است. از بعد محاسباتی، روش SB RAB برای حل دو سری از مسائل مبنای موجود در ادبیات مسیریابی وسیله نقلیه مورد استفاده قرار گرفته و نتایج آنها گزارش شده است. همچنین، این مسائل مبنا از روش مرسوم در ادبیات حمل ونقل یعنی روش تفکیک شبکه به دو زیر بخش مسیریابی وسیله نقلیه و حمل ونقل چند وجهی نیز حل و نتایج مربوطه گزارش شده اند. در انتها، با مقایسه همه نتایج، نشان داده شده که روش SB RAB می تواند جواب هایی برتر در مدت زمانی قابل قبول ارایه دهد.
    کلیدواژگان: حمل ونقل چند وجهی، مساله مسیریابی وسیله نقلیه، حمل ونقل دریایی، مسیریابی وسیله نقلیه چند تحویلی
  • سید مهدی زهرایی، حبیب سامی صفحه 319
    اگرچه تنها بیش از دو دهه از کاربرد جداسازی لرزه ای در پل ها می گذرد، اما مطالعات بسیار زیادی در این زمینه صورت گرفته است که همگی کارآیی آنها در پل ها را تایید می کنند. در این تحقیق عملکرد لرزه ای پل های موجود با تکیه گاه های نئوپرن انبساط حرارتی و امکان کاربری جزئی و محدود آنها برای جداسازی لرزه ای پل ها، به صورت تحلیلی بررسی می شود. بنابراین ابتدا کارآیی جداسازی لرزه ای را با تحلیل دینامیکی غیر خطی تاریخچه زمانی دو نمونه پل متداول بزرگراهی که توسط چهار نمونه جداگر الاستومریک جداسازی شده است، اثبات کرده و نتیجه گرفته می شود که جداسازی لرزه ای ضمن کاهش پاسخ های لرزه ای، نیروی زلزله را بین کوله ها و پایه ها به صورت متعادل توزیع می کند. پل های مورد بررسی در حالت معمولی (با تکیه گاه های انبساط حرارتی و بدون تکیه گاه های انبساط حرارتی) نیز مدلسازی و تحلیل شده اند. نتایج تحلیل نشان می دهد که کارآیی تکیه گاه های موجود انبساط حرارتی در کاهش پاسخ های لرزه ای مناسب نبوده و حتی در صورت امکان لغزش لازم و تحمل کرنش های برشی بزرگ در آنها به هنگام زلزله، به علت الاستیک خطی بودن رفتار نیرو- تغییرمکان، میرایی و استهلاک انرژی چندانی نداشته و نمی توانند از سطح انرژی زلزله و نیروهای برشی وارد بر زیرسازه پل ها به میزان قابل ملاحظه ای بکاهند، در صورتی که سهم جداگرها در جذب و استهلاک انرژی ورودی زلزله بیشتر از 50% است. بر اساس نتایج این تحقیق، نسبت کارآیی این تکیه گاه ها به جداگرهای لرزه ای برای کاهش نیروی برشی ناشی از زلزله، بین 30 تا 50% تعیین شد
    کلیدواژگان: جداسازی لرزه ای، تکیه گاه انبساط حرارتی، استهلاک انرژی، جداگر الاستومری، تحلیل غیر خطی تاریخچه زمانی
  • رضا سمیع زاده، سید کمال چهارسوقی، سعید جهانیان صفحه 333
    یکی از عوامل اساسی در رشد سطح کیفیت زندگی افراد در جوامع امروزی بی شک بهبود خدمات نقل و انتقالات عمومی است. بالا بردن کیفیت ارایه خدمات حمل و نقل نیازمند افزایش میزان هماهنگی در فرآیندها و همچنین برقرار ساختن امکانات دسترسی سریع تر و آسان تر افراد به این گونه خدمات است. تجارت الکترونیکی با توجه به توانایی ها و امکانات خود می تواند به عنوان بستری جهت تقویت و تکامل فرآیندهای حمل و نقل عمومی در نظر گرفته شود و به این ترتیب ورود شرکت های حمل و نقل عمومی به تجارت الکترونیکی به عنوان گامی جهت تقویت و تکامل فرآیندهای حمل و نقل عمومی در نظر گرفته می شود. در این پژوهش با توجه به مطالعه مدل های ورود به تجارت الکترونیکی و تحلیل آنها، نسبت به تعیین مدل مناسبی برای ارزیابی عملکرد شرکت های حمل و نقل در ورود به تجارت الکترونیکی اقدام شده است و با استفاده از مدل به دست آمده یک شرکت حمل و نقل عمومی (شرکت رجاء) مورد ارزیابی قرار گرفته است. به منظور ارزیابی عملکرد شرکت رجاء از ابزار پرسشنامه جهت جمع آوری داده های مرتبط استفاده شده و برای تحلیل داده ها، روش تحلیل مسیر1 که توانایی تعیین میزان تاثیر گذاری هر یک از متغیرهای مدل را بر عملکرد شرکت دارد، بکار گرفته شده است. با توجه به تحلیل داده های جمع آوری شده، شاخص های مؤثر بر عملکرد تجارت الکترونیکی شناسایی شده اند. به این ترتیب با استفاده از این شاخص ها چارچوبی جهت ارزیابی عملکرد شرکت های حمل و نقل عمومی در ورود به تجارت الکترونیکی به دست آمده است.
    کلیدواژگان: شرکت های حمل و نقل عمومی، تجارت الکترونیکی، کارت امتیازی متوازن
  • محمود عامری، علیرضا خاوندی صفحه 349
    حد تحمل، به بیشینه کرنش یا تنشی اطلاق می شود که مصالح می توانند در آن حد، تعداد بی نهایت سیکل بارگذاری- باربرداری را تحمل کنند. آگاهی از مقدار حد تحمل مخلوط های آسفالتی باعث می شود تا ضخامت لایه آسفالتی بیش طراحی نشود. این موضوع به ویژه در روسازی های با عمر بالا1 (40 سال) به دلیل طرح بهینه ضخامت لایه آسفالتی، اهمیت زیادی دارد. در چند سال اخیر مطالعات مختلفی توسط محققین برای تعیین حد تحمل مخلوط های آسفالتی انجام شده است. در این مقاله، با استفاده از آزمایش تیر خمشی چهار نقطه ای، حد تحمل انواع مخلوط های آسفالتی بر مبنای معیار کاهش سختی به میزان 50 درصد و پارامتر «نسبت تغییر انرژی تلف شده» مورد بررسی قرار گرفته است. همچنین با استفاده از نتایج حاصل از این بررسی و بر اساس مشخصات مخلوط آسفالتی نمونه های آزمایش شده، رابطه ای برای پیش بینی حد تحمل خستگی این مخلوط ها پیشنهاد شده است.
    کلیدواژگان: ترک های خستگی، عمر خستگی، حد تحمل، تیر خمشی چهار نقطه ای، نسبت تغییر انرژی تلف شده
  • یگانه موسوی جهرمی، منصوره عبادتی فرد صفحه 361
    هدف از این مطالعه، بررسی اثر سرمایه گذاری دولت در زیرساخت حمل و نقل بر سرمایه گذاری بخش خصوصی و رشد اقتصادی ایران است. در این مطالعه، با توجه پژوهش های انجام شده در کشورهای در حال توسعه، از مدل شتاب انعطاف پذیر برای تابع سرمایه گذاری بخش خصوصی و از الگوی رشد سولو همراه با تعدیلاتی برای رشد اقتصادی استفاده شده است. متغیر سرمایه گذاری در زیرساخت حمل و نقل از عوامل تعیین کننده موجودی مطلوب (*k) در مدل سرمایه گذاری بخش خصوصی در نظر گرفته شده است. در مدل رشد، دو متغیر سرمایه گذاری دولت در بخش حمل و نقل و سایر بخش ها به عنوان یکی از نهاده های تولید در کنار نیروی کار و سرمایه گذاری خصوصی وارد تابع تولید شده است. در تخمین مدل سرمایه گذاری از روش متغیر ابزاری و در مدل رشد از روش OLS استفاده شده است. نتایج برآورد مدل های مذکور طی سالهای 1338 الی 1382 نشان می دهد که رابطه قوی بین سرمایه گذاری در زیرساخت حمل و نقل و سرمایه گذاری بخش خصوصی وجود دارد. همچنین با توجه به کشش مثبت به دست آمده برای سرمایه گذاری در حمل و نقل، سرمایه گذاری در این زیرساخت اثر مثبت و معناداری بر رشد اقتصادی کشور دارد. با در نظر گرفتن نتایج حاصله، افزایش سرمایه گذاری دولت در زیرساخت حمل و نقل پیشنهاد می شود
    کلیدواژگان: زیر ساخت حمل و نقل، سرمایه گذاری دولت در حمل و نقل، سرمایه گذاری بخش خصوصی، رشد اقتصادی و سرمایه گذاری دولتی
  • یادداشت پژوهشی
  • یونس نیازی، مرتضی جلیلی قاضی زاده صفحه 373
    تغییر شکل های دائمی (شیارشدگی) یکی از مشکلات اساسی در مخلوط های بازیافتی است و معمولا این خرابی در مقایسه با روسازی های آسفالت گرم زودتر اتفاق می افتد. برای رفع این مشکل از افزودنی هایی نظیر سیمان و آهک در مخلوطهای بازیافتی استفاده می شود. در این تحقیق از سیمان پرتلند و آهک به عنوان دو نوع افزودنی که در بازیافت آسفالت به روش سرد با امولسیون قیر بیشتر بکار رفته اند، استفاده شده است. سیمان پرتلند به صورت پودر و آهک به دو صورت دوغاب آهک و پودر آهک شکفته به مخلوط افزوده شد و تاثیر هر کدام بر تغییر شکل های دائمی مخلوط های بازیافتی با استفاده از آزمایش های مارشال، ضریب برجهندگی، خزش دینامیکی و ماشین اثر چرخ (ویل تراک) مورد بررسی قرارگرفت. همچنین مقایسه ای بین این دو نوع افزودنی انجام شده است. نتایج به دست آمده در این پژوهش حاکی از آن است که میزان تغییر شکل های دائمی مخلوط های بدون افزودنی نسبت به مخلوط های حاوی سیمان و آهک بسیار بیشتر بوده و افزودن سیمان پرتلند و آهک باعث افزایش قابل ملاحظه مقاومت در برابر تغییر شکل های دائمی مخلوط های بازیافتی و در نتیجه کاهش شیارشدگی می شود. بیشترین کاهش در تغییر شکل های دائمی مربوط به نمونه های حاوی سیمان و دوغاب آهک است که کاهشی حدود 50% را نسبت به نمونه های بدون افزودنی نشان می دهد. نظر به نتایج به دست آمده و این که نحوه افزودن سیمان در قیاس با دوغاب آهک از سهولت بیشتری برخوردار است استفاده از سیمان برای کاهش تغییر شکل های دائمی در مخلوط های بازیافتی پیشنهاد می شود.
    کلیدواژگان: مخلوط های آسفالتی، بازیافت سرد، افزودنی های سیمان پرتلند و آهک و امولسیون قیر
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  • P. Bazdar Ardebili, A. Rezaiee Arjroudi Page 295
    In analyzing the macro economics issues, investing in transportation sector in order to job creation has paramount importance.In this paper, the role of investment on job creation in transportation sector is estimated and analyzed based on dynamic approaches regarding - labor demand and cointegration. For estimating the model, statistical data within the period 1350-1381 have been be used. Results show that primarily the cointegration models variables are recognized, then structural models and the optimal number of orders will be specified.In the next step, the number of co-integration vectors are determined and finally, the relationship between investment and labors demand in transportation sector are estimated. In order to join the long term balanced relationship among variables with short term fluctuations, vector error correction model related to balanced relation, will be estimated for variable employment in transportation.Among of different models of labor demand, the best model is "scientific model" which is estimated from the following relationship: LD = shows the number of job applicatorAK= Total number of investmentK= The current amount of investmentPK= Utilization of investmentU= disturbance of timeT= TimeThe results shows that the more labor demand, the more increased investment. Based on this method, if the investment in transportation increased to 1 million, the number of labor demand in transportation sector will be increased only to 19 percent.On the other hand, %19 ×1000= 19, means that creating a new job in transportation sector demands 52.63 Million Rail investment. By creating a new job, 621 persons will be employed at new jobs.According to achieved analytical results and based on vector error correction model, the following result may be concluded.The transportation sector having the development strategy regarding two inputs (labor demand and investment) will have no substitutes for the labor demand and there will be no reduction in the manpower.
  • Y. Rabbani, M. M. Sepehri, S. H. Zegordi Page 307
    What has initiated the idea of this research is the situation of marine, rail and road transportations in the south region of Iran, the Persian Gulf and Oman see. There are a few large Iranian ports in the region (e.g. Imam Khomeini and Shahid Rajaee) that have been equipped to serve large containerships while, most of the other ports either have not been developed or their geographical and topological restrictions do not let them to serve large ships. For instance, Abadan and Khorramshahr were two active ports and main Iranian Import/Export terminals until the Iraqi army attacked them in 1981. Although, the war finished in 1989, nowadays these are unable to serve current fleet of large container ships due to the limitation of their water way, the Arvand-River. Therefore, their rail and road transportation system's capacity are mostly unused. On the other hand, due to the national economic development programs and the especial attention to the Iranian 20 year's economic vision, Iran needs to develop continuously new transportation capacities as well as better utilization of the existing capacities. To develop the transportation capacity, one way is to invest on the existing ports in order to serve larger ships. However, in one hand, the investment should continuously grow because, as the literature shows, mega-ships and rapid-ships are going to emerge until the year 2020. On the other hand, some of the ports, due to their geographical situation, are not able to catch any share of those investments. Therefore, we need to find a way to activate the small ports to use their capacities.A way that could be theoretically investigated is that the large ports could be used as hobs (intermediate centers) to feed the transportation network (include small ports and ships). In this case, it might be possible to plan a rout for a mega-ship which comes from a depot (outside the region, such as the sought east of Asia) so that it discharges goods at some ports in the region (the Iranian and other nation ports in the Persian Gulf, Oman Sea and the Mouth of Indian Ocean), and then set back to the depot. Consequently, the discharged goods are handled to some consumer centers (the centers in Iran as well as the transit destinations like: Afghanistan, Iraq, Turkey, Russia, and the new independent countries in north of Iran) by a multimodal network (with road, rail and marine modes). Applying this idea could brisk up the utilization of the Iranian private fleets and ports in the region. That is because in one hand, there are plenty of small and medium size ships (that are mostly private ones), which could provide us with a large amount of marine capacity among Iranian and other nations ports in the region. On the other hand, most of the Iranian ports are not able to serve large ships. Moreover, some of the countries in the region (e.g. Pakistan and the Arab Emirates) have extensively invested on some of their ports, so those ports could be used to brisk up utilization of the Iranian fleets and ports and to increase the transit of goods through Iran. In this case, an opportunity rises to get advantage of other nations capitals in order to speed up the flow of goods to/from Iran. However, in order to get advantage of this opportunity, its feasibility, conditions, benefits and other political and social aspects should be studied. This paper concerns with studying the network aspects of the idea in order to evaluate its costs and possibly optimize them. From the network design point of view, the network among the depot and the intermediate ports of the marine transportation network could be considered as a Split Delivery VRP (SDVRP) except than that the demands of the customers (the intermediate centers) are not known in advance, and they are variables to be decided. In the split delivery vehicle routing problem (SDVRP), a fleet of homogeneous vehicles should serve a set of customers, while each customer can be visited more than once, contrary to the assumption in the VRP. So, the demand of each customer can be greater than the capacity of the vehicles. No constraint on the number of available vehicles is considered. Moreover, the network among the intermediate and the consumer centers is a multimodal transportation one in which the goods supplies at the intermediate centers are not known in advance and they are variables to be decided. In this network, it is possible to change the mode of transportation at some of the intermediate or consumer centers with some charges. In this paper the idea has been introduced and, a general transportation system based on it has been originally designed and modeled. The system consists of a Split Delivery Vehicle Routing contiguous to a Multimodal Transportation. The system has originally been modeled and solved in this paper using exact and heuristic methods. The branch-and-bound technique has been used to solve small size test problems. Moreover, in order to solve larger size instances, a heuristic method, called SB-RAB, has been developed which works based on limited entry Simplex method. SB-RAB has been applied to solve two series of test problems which have been barrowed from the VRP literature. Both exact and SB-RAB algorithms are then applied to solve a series of problems which has been adapted in this paper from a set of VRP benchmark problems. Finally the results have been compared and show that the SB-RAB is able to produce good quality solutions in an acceptable time.
  • S.M. Zahrai, H. Sami Page 319
    Efficiency and benefits of seismic isolation as a passive control allow designers to reduce and balance the earthquake forces imposed to bridge piers and abutments. Regarding the variety of bridge damages occurred in the past earthquakes, mostly as a result of underestimation of seismic forces, seismic isolators can be effectively used in designing or retrofitting of bridges in high seismicity zones. Numerous existing bridges in the country use expansion bearings between superstructure and substructure. To mitigate the impact of seismic forces and increase bridge safety during earthquakes, these bearings can be easily replaced with seismic isolators.Although seismic isolation has been used for only two decades, extensive studies conducted in this field altogether confirms the efficiency of seismic isolation in bridges. The objective of this paper is to briefly review seismic isolation and its application in bridges to reduce earthquake forces in order to encourage their use in the country, and to investigate the shortcomings of existing expansion bearings. For this purpose, seismic isolation efficiency of two typical kinds of high-way bridges that are isolated with four elastomeric isolators is investigated by nonlinear earthquake time-history analysis. It is concluded that elastomeric isolators are very effective in reducing seismic forces and displacements of the typical bridges. Changing the vibration nature of the bridges, isolators can decrease the earthquake lateral force level and protect the non-ductile substructure elements through deviating and absorbing a major part of input seismic energy. The larger the lateral stiffness of the bridge (like bridges with smaller spans and shorter piers), the more effective the seismic isolation. In addition to reducing seismic responses, seismic isolation, distributes earthquake force equally among piers and abutments. However, by decreasing the elastic stiffness of isolator, bridge responses including lateral drifts and internal forces reduce more, while the absolute displacement of the deck increases. This issue can be compensated by increasing yielding force and damping of the isolators by inserting other types of devices. Elastic stiffness as well as yielding force of isolator by controlling the hysteretic damping are important factors. Moreover, to get familiar with the seismic performance of existing bridges having expansion bearings, and to identify their limited and inadequate application as seismic isolation in bridges, their seismic behavior is studied and restricted use of such bearings for seismic isolation of bridges is numerically investigated. For this purpose, investigated bridges (with or without expansion bearings) are modeled and analyzed with “SAP2000 Nonlinear” subject to different earthquakes.Results show that expansion bearings effectiveness in reduction of seismic responses is not sufficient as seismic isolators. Furthermore, even in case of having enough slip during earthquakes, corresponding damping and energy dissipation of expansion bearings would be small due to their linear elastic behavior for force-displacement relationship. As a result, incapability of expansion bearings in tolerating large shear strains and absorbing input earthquake energy, because of damping shortcoming, reduces their efficiency as seismic isolators.For optimum application of seismic isolation in new bridges and also for retrofitting existing bridges, it is highly recommended to do research on manufacturing elastomeric isolators reinforced with steel plates or fiber polymers to induce high damping and use them instead of typical neoprene expansion bearings.
  • R. Samizadeh, S. K. Chaharsough, S. Jahanian Page 333
    Improving public transportation services is one of the major factors for enhancing the quality of people's life in today's societies. The quality enhancement of transportation services requires increasing coordination in processing and also providing the people with the easiest and the fastest ways to access the services.Given its potentialities, the e-commerce can be considered as a base for improving and evolving the public transportation processes. Thus the e-commerce adoption by public transportation companies is regarded as a step towards enhancing their processes. This paper regarding the models of e-commerce adoption and their analysis provides a proper model for appraising the performance of the transportation companies in e-commerce adoption. One of the public transportation companies (RAJA), a leading company in e-commerce adoption, has been examined in this paper using the provided model in order to apprise its performance. Questionnaires have been used for data gathering and for analyzing the collected data, Path analysis has been used to set the effects of the model variables on the performance of the company. By analyzing the gathered data, the effective indicators influencing the performance of e-commerce have been identified. Thus, using these indicators, a framework for appraising the performance of the public transportation companies in e-commerce adoption has been provided.
  • M.Ameri, A.Khavandi Page 349
    Fatigue cracking is one of the most prominent distresses in asphalt pavement. Considerable research has been done to develop theoretical models, experimental laboratory testing techniques, and data analysis methods to predict the fatigue performance of asphalt paving mixtures. The majority of fatigue studies were conducted in order to determine the curves and relationships that are called the transfer functions.Usually, the transfer functions are given based on the test results conducted in more than 250 micro strains. But in long life pavements, we need to examine the behavior of asphalt mixtures in lower strains. Long life or the perpetual is defined as more than 40 years without any major structural failures or repairs.These pavements have three asphalt layers. The surface layer and the middle layer should have the high rutting resistance and the lower layer should have enough fatigue resistance so that there would not be any failure during operating the asphalts. As per these characteristics, and high rate of passing traffic during operating the asphalt, these kinds of pavements need an asphalt thicker layer compared to common pavements. The requirement made the designers to find an optimized thickness which is either economical or has suitable serviceability during operating period without the need to be prepared. To prevent the failure caused by the fatigue of the lower layer, it is very important to find the strain level below which no fatigue damage occurs. This strain level is called "endurance limit".The endurance limit is level of strain below which fatigue damage does not occur for any number of load repetitions. The concept of the endurance limit was originally examined and developed for the metal materials but the asphalt mixtures (Viscoelastic materials) were studied less than the latter.That is a valid concept for hot mix asphalt and its quantifications could contribute in the efficient design of long life flexible pavements with a significantly reduced life cycle cost. In the recent years, some researchers have conducted various studies to determine the endurance limit of hot mix asphalt. In 1972, Monismith and Mclean first proposed an endurance limit of 70 micro-strain for asphalt pavement. It was observed that log-log relationship between strain and bending cycles converged at approximately 70 micron-strain at approximately 5 million cycles.In 2000, Carpenter et al, based on the fatigue tests results in different levels of strain, observed that an obvious difference happens in the asphalt mixtures behavior, more than 1.1E+7 in the fatigue life.In 2006 based on Brown et al study, by conducting the traffic studies, a mix which provided 50 million cycles or more, was considered to be below the endurance limit.In this paper, using four - point flexural bending beam test, the endurance limit of different types of asphalt mix based upon 50-percent stiffness reduction and the parameter "dissipated energy change ratio" were investigated. Comparing the result of two methods shows that the fatigue life based on the "Rate of dissipated energy change" criterion is more than the result of the 50-percent stiffness reduction (direct or extrapolation method). Using the criterion suggested by Carpenter (11 millions of loads repetition) and the criterion suggested by Brown (50 millions of load repetition), the endurance limit has been determined for all the tested samples. The endurance limit for all the samples based on the fatigue life resulted from "plateau value" is between 400 to 1000 micro-strain. And the fatigue life based on the stiffness reduction criterion is between 200 to 700 micro-strains. Based on the result of this study, for every type of asphalt mixture, the number of load repetition curve-strain was drawn and the behavior change section was determined for each type of asphalt mixture. The strain corresponding with section can be considered the mixture endurance limit. This is a method for determining the endurance limit corresponding with the concept suggested by Carpenter but separately, the special behavior change section is determined for each type of asphalt mixture. As per the suggested method, the endurance limit of the asphalt mixtures types is between 160 to 270 micro-strains. The results show that the endurance limit depends on the asphalt mixture characteristics.Also using the results of tests and the characteristics of tested specimens, a relationship has been suggested for predicting the endurance limit of hot mix asphalt. This relationship shows that increasing the bitumen percentage and reducing the asphalt mixtures air voids, the endurance limit will be increased. Also, increasing bitumen penetration grade for increasing the fatigue life of the asphalt mixture is a positive effect. Also, increasing the nominal size of materials and the percentage of fine materials and filler in the asphalt mixture cause increased value of the endurance limit.
  • Y. Mousavi Jahromi, M. Ebadati Fard Page 361
    Based on the published information by Iranian Bank Markazi (Central Bank of Iran), the share of investment in transportation sector increased from 11.04 to 22.27 percent over the period 1372 (1993) to 1382 (2004). It seems that Iran's transportation sector has been in the duration of capital accumulation. Since the development of this sector is very expense intensive, it is necessary to study how investment in transportation influences the macroeconomic variables. Hence, in this study we investigate the effects of government spending or public investment in transportation on private sector investment and economic growth in Iran. In other words, we respond to the two following questions considering the mentioned period (1993 - 2004):1- Does public investment in transportation crowd out private sector investment?2- Is there a positive relationship between public investment in transportation and economic growth?There are conflicting evidences in the literature regarding the question "How the public investment affects private investment?". Some of them indicate a positive relationship between public and private investment [Sundrajan & Thakur (1980), Green & Villanueva (1990), Abdoli (1374)]. The others, due to restriction of resources, present a negative relationship (Blijer & Khan, 1984). In this study, regarding the accomplished researches in developing countries and Iran economic specifications, an adjusted flexible accelerator model to study the private investment function is used. In addition, according to the purpose of this study we consider private investment as a function of the following variables:- First-differential variables including: gross domestic product (regardless of oil sector), real financing facilities granted to the private sector by banks, oil export, public investment in transportation and public investment in other sectors.- Gross investment and capital stock in the previous year.It is remarkable that real financing facilities granted to the private sector by banks is considered as a proxy for the interest rate that is determined by government. Finally, private investment function is estimated based on annual data from 1994- 2003 via the instrumental variables method, after omitting two independent variables, first-differential of oil export and public investment in other sectors. There are two types of researches for studying the relationship between public investment in transportation and economic growth:First, public investment is considered as one of the inputs in the production function [Aschauer (1989), Munnel (Feb. 1990), Holtz-Eakin (1994)].Second, the causal relationship between public investment in transportation and economic growth is investigated [Easterly& Reblo (1993), Devarajan (1996), Emranul Haqu & Dong Heon Kinm (2003), Molashahi (1382)].In order to study the mentioned relationship we acquire Neo-Classic growth model and Khan & Rainhard (1990) approach. We develop that model by adding investment in transportation infrastructure as a component of production function. In our growth model we consider two variables, public investment in transportation sector and public investment in other sectors as inputs of production function, along with labor force and private investment variables. This model is estimated based on annual data from 1339 to 1382, by using the OLS method.This empirical study is based on data from Management and Planning Organization and Central Bank of Islamic Republic of Iran. Estimations and statistical tests indicate that there is a strong relationship between public investment in transportation and private sector investment. Positive and high elasticity of public investment in transportation shows that investment in this infrastructure has a significant positive impact on economic growth in Iran. But we should not ignore that achieving such results is due to the existence of necessary conditions for economic development such as: 1-access to production resources2-investment conditions related to scale, location, time, and the network affects3-political and organizational conditions in relation to financing methods, legal policies and decisions for investment in local, regional, and national levels of transportation.Regarding discussed issues, the study of various influences made by the development of this infrastructure (transportation) on the economic variables may be used as contributing guidelines for the policy analysts. At the end, the study on different levels of location (local, regional, and national) and period (short, intermediate, and long run) or combinations of them are suggested for future research with similar topic.
  • Y. Niazi, M. Jalili Ghazizadeh Page 373
    Cold in-Place recycling (CIR) has been effective at rehabilitating the aged pavements, and many agencies have used asphalt emulsions for CIR in their projects with good results. However, some emulsion CIR projects exhibited rutting, thermal cracking and asphalt stripping problems, leading agencies to use Portland cement, lime and class C fly ash as additives to prevent early rutting and stripping problems. Due to lack of previous studies on applying additives in CIR mixes, in this study we used Portland cement and lime as additives. The Portland cement was introduced in powder form and lime was utilized as hydrated lime in powder form and lime slurry, and the effects of each additive on permanent deformation of CIR mixtures have been evaluated. The objectives of this study were to evaluate the effects of lime and Portland cement on permanent deformation of CIR mixtures with asphalt emulsion and comparing the effects of these two additives. A laboratory study was undertaken to evaluate the effect of Portland cement and lime on permanent deformation of CIR mixes. The mixtures were tested for Marshall Test (ASTM D 1559), resilient modulus (ASTM D4123), and Dynamic creep test: BS-DD226, Wheel track test: BS 598:Part110:1996.The results showed that:1. Addition of Portland cement and lime increases the Marshall Stability and bulk specific gravity and reduces void content and flow of the recycled mixtures. The use of Portland cement resulted highest stability values.2. The use of HLS, HL, and Portland cement result in significantly increase in resilient modulus values. Use of HLS and Portland cement resulted in more resilient modulus values than HL. The use of 2% Portland cement resulted highest resilient modulus value since Portland cement stiffens the binder.3. The results of dynamic creep test show that the use of Portland cement and lime resulted decreased rut depth. The use of Portland cement, HLS and HL resulted in a reduction in rut depth of 40, 30 and 26% as compared to sample without additives respectively.4. The results of wheel track test show that the samples without additives have the most rutting potential. The addition of 2% Portland cement, 2% HLS and 2% HL resulted in a reduction in rut depth of 58, 50 and 38 as compared to sample without additives respectively.5. Both dynamic creep and wheel track tests show that addition of Portland cement and lime can reduce the permanent deformation of recycled mixtures. The best additive for reducing permanent deformation proved to be Portland cement. Cement acts as a secondary binder in cold mix. Hydration is necessary to activate the cement and this can only occur in the cold mix material in which water is available. In the absence of water, cement merely acts as an inert filer. It is also well known that the hydration reaction of cement can cause a noticeable temperature rise in concrete mixtures. The effect of heat of cement hydration on bituminous emulsion mixtures may also be significant. A rise in temperature would increase the rate of reaction between aggregate and emulsion and, if large, could increase the rate of water evaporation from a mixture. Both of these effects could increase the breaking rate of the emulsion and the curing rate of the mixture.6. Use of Portland cement and lime slurry had better results than hydrated lime but due to the difficulties in producing lime slurry in practice, the use of Portland cement is recommended.