METHODS OF COMPARISON STEEL AND REINFORCED CONCRETE STRUCTURE S ON EXAMPLE OF A ONE-STOREY, SINGLE-SPAN FRAME Elżbieta Szafranko Univerity of Warmia and Mazury in Olztyn, Faculty of Technical Science, Olztyn, Poland Abtract In the civil engineering practice, there are many way of completing contruction invetment project. Each contruction can be built in a number of way, which enable architect and deigner to prepare different variant of planned building. Selection of a technology employed to raie a building object i one of the mot important deciion to be made while planning an invetment project. The problem ha been preented on a model of frame with full column and a mono-pitch pandrel beam with the olid cro-ection, made a a teel and monolithic reinforce concrete contruction. Key word: analyi of contruction project, managing a contruction project, comparion of the tructure 1. INTRODUCTION In engineering practice we have an opportunity to chooe between different technologie of contruction work and between different material (Giżejowki et al. 2010).. Wihing to achieve economically atifying olution while meeting all other requirement that building contruction hould fulfill, comprehenive analye are made, baed on different election criteria. The fundamental requirement mot often comprie: reliability of the contruction and it ueful life, technological criteria, which depend on the ued material, machine, production procee, availability and the poibility to tranport material and contruction element to the contruction ite, functionality of the building, depending on it ize and pecific feature, economic criteria, which define the cot indice, epecially the cot of contruction work, the maintenance cot once it i erected, conumption of material, total weight, hare of indutrialized olution in the contruction proce, durability and value of material recovered once the ueful life of a building i over, legal conideration, impoed by the law binding in the area where a given building invetment i planned and executed, formal iue, uch a impoed norm and tandard, ergonomic and ethetic problem, to which invetor and future uer of the building pay pecial attention, ecological quetion, regarding the impact of an erected contruction on the urrounding natural environment (Tarnowki 1997) While checking off the above criteria, it i important to bear in mind that the reliability and afe ue of a building object are two eential objective. A contruction which fail to atify thee condition i automatically dicarded. Having to fulfill all the above condition, a deigner face an immene challenge. Apart from knowing the fundamental deign rule and principle, they hould alo be familiar with the current contruction market, the latet technological olution and poible future development o a to be able to jutify the choice they make for a given contruction deign (Bentz, Collin 2004),. Thi article dicue comparative analytical method applied to analyze variant contruction olution, uing a a cae a choice between a teel and ferroconcrete one-tory ingle-pan frame with full column and a mono-pitch pandrel beam (Ajdukiewicz 2011). 2. DESCRIPTION OF A MODEL CONSTRUCTION A model of a one-torey, ingle-pan frame with full-walled column and a mono-pitch pandrel beam with a full and olid cro-ection along it entire length, bearing a uniform bracing load of the roof tructure and external 328
force applied to the roof and the wall (Grabiec et al. 2001). For comparion, it wa aumed that the contruction would be made of teel and of reinforced concrete. In the preented cae, for both the teel and the reinforced concrete contruction, it wa neceary to aume that all joint are rigid becaue uch i the type of joint made in a monolithic contruction. The following baic parameter were aumed: - a variable pan length, that i the centre to centre pan between oppoite column, - a fixed longitudinal pan of the frame, - a fixed lope of the pandrel beam, and conequently variable height of column with the variable pan and contant height of the contruction. The decribed contruction i compoed of the column and the pandrel beam. With the aumed work of the contruction, the horizontal element are ubjected to bending and hearing. In the ferroconcrete contruction, the centre to centre pan wa determined depending on the adopted condition, with the adequate dimenion typically maller than 25% of the pan of ymmetrically reinforced beam; when deigning the teel pandrel, HEB I-beam were ued. The decribed tructure ret on column anchored in foundation bae whoe height depend on the roof lope angle. The column are the main element expoed to compreion and tranfer all force to element of the foundation. Same a in the cae of horizontal element, the dimenion of the centre to centre tranvere ection of a ferroconcrete contruction ocillate within a quarter of the pan, and the reinforcement i ymmetrical; in the teel contruction, it i made of I-beam. Figure 1 how a deign of the contruction. Fig. 1. Computational deign of the analyzed contruction, Source; the author The following contruction wa taken for the calculation: a middle flat frame of a ingle-pan hall with an inclined pandrel beam and a contant lope angle of the roof equal 5 o, with the contant height at the highet point of the interection of the column and pandrel beam equal 6 m and the longitudinal centre to centre pan of the frame equal 6 m. The tranvere ditance between the column will be variable, from 6 m to 18 m at 2-m interval. The analyzed building will tand in the IV now zone and I wind zone according to the Polih tandard. The external column are expoed only to wind, auming the wall are caed. The length of the hall wa aumed to equal n x 6 m, a the analyi comprie only the middle frame and an infinite length of the building affect only the wind load calculation, which implifie it value to a contant for different width of the aile in the particular variant. Below, reult of olution for individual et of frame are preented in the form of the mot optimal with repect to their trength - teel and reinforced concrete cro-ection for particular element of the frame, which will erve a a data bae for further economic and technical conideration. In the table, depending on the pan of the aile, cro-ection of pandrel beam and column are divided, but the latter are conidered identical in each cae, be it the right or the left column. 329
3. TRADITIONAL METHODS OF ANALYZING BUILDING STRUCTURES Among the baic traditional method i an approach in which parameter of the conumption of material and unit cot are calculated and juxtapoed. The firt i the ratio of the volume of reinforced concrete to teel, in appropriate tandard unit, ued in a given tructure (Górki, Hojarczyk 1970). Z= [m 3 ] reinforced concrete / [t]teel [1] It reflect the ratio of variant conumption of individual material to erect the ame building object, e.g. when a teel tructure i choen, and the ued material equal 10 kg per the cubic capacity of the building, or when 0.05 m 3 of reinforced concrete i ued, the parameter i equal 5. A revere equivalent would be the quotient of the unit price of compared material. N= unit price of ferroconcrete tructure unit price of teel tructure The reult of thi imple analyi i the product of the above parameter. If the Z x N quotient i more than one, then the teel tructure in the analyzed building object i le expenive in term of ued material. Such comparion can alo be made with repect to other outlay, uch a engaged equipment or labour (Górki, Hojarczyk 1970) While analyzing potential applicability of the above method, it appear than we can compare tructure of a given function built from uitable material, by comparing weight and trength characteritic of different type of teel or concrete. For example, a compreed element made of teel or concrete, it i poible to derive a formula for Z equivalent: auming that element achieve maximum trength, we tranform the formula for the trength of a ection ubmitted to with concentrated force. [2] V G b Q fd A = [3] Q L = - in the cae of concrete, we need the volume ued in the analyzed element f b d Q L γ f = - in the cae of teel, we need the ued weight d where: Q - force compreing the element, A - cro-ection of the element, f d - calculated compreion trength ( b fd for the concrete and fd for the teel element), L - length of the element, b V - volume of the concrete element, G - weight of the teel element, γ - volumetric denity of teel. If we aume in the above formula that the product Q L i the ame in both cae, we arrive at the final formula to calculate equivalent Z b V 1 fd Z = = [4] b G f γ Below, in table 1 we preent example of Z equivalent for ome clae of concrete and type of teel, which viualize the difference originating from propertie of given material in the analyzed work of a compreed cro-ection. d 330
Stael Concrete Tab. 1. The comparative index Z of reinforced concrete and teel for a compreed element * b f d [MPa] S185 S235JR S275JR S355J2 f d [MPa] 165 205 225 295 C16/20 11,43 1,84 2,29 2,51 3,29 C25/30 17,86 1,18 1,46 1,61 2,10 C50/60 35,71 0,59 0,73 0,80 1,05 C80/95 57,14 0,37 0,46 0,50 0,66 * reult in the table were computed for the teel volumetric denity equal 7850kg/m 3 Naturally, the reult in the table are approximation of actual reult. However, although they lack the ideal preciion of calculation, thi method of comparion generate reliable reult and can erve a a preliminary evaluation of a planned contruction, auming that ame load capacity of the tructure made from different material i enured. Another method (Górki, Hojarczyk 1970). to compare cot of tructure built from different material i the one where the cot ration index i calculated for aembled contruction made from different material: where: a G a [ ( 1)] [ ( 1)] an + nc pcs ps ψ = + = c S S i = - expreed the proportion of weight of tructure made from i th material, G i + 1 c+ w+ m S = - i the ratio of the total cot of a unit quantity of the firt material (c), c workhop labour (w) and cot of aembling (m) element to the cot of material a uch wi + mi p = w + m i c i + 1 i+ 1 i+ 1 - expree the ratio of workhop labour (w) and aembly cot (m) of the i th material, c n = - expree the proportion of cot of i th material. The above method doe not include maintenance cot, which may differ from one tructure to another, but for the ake of our ubequent conideration, it wa aumed that thi type of comparion will uffice to decribe the et target of the analyi. [5] 4. MODERN METHODS OF ANALYSIS OF COMPARATIVE CONSTRUCTIONS In modern engineering practice in the analyi of the tructure often are preented other apect than it once wa. Currently, the greatet emphai i placed on the broad ene an economy. Such area a conumption of material, time of contruction work and aociated cot of contruction are being increaingly important (Saaty 1990). 331
4.1. Conumption of material and technology Nowaday, when planning invetment project, much emphaize i laid on the ue of material. Thi tendency i congruent with the ecological approach to the contruction indutry, aving raw material, decreaing the tranportation load and enuring that the invetor can attain financial aving. F l o r a r e a S t e e l c o n c r e t e F o o t p r i n t Fig. 2. Cot of ued material per 1 m 2 of the floor area of a building depending on the footprint The diagram illutrating dependence between cot of material and footprint ha been drafted baed on the author own calculation. The diagram how an evident advantage of a ferroconcrete tructure over a teel one. Fig. 3. Comparion of cot of ued material per 1m 2 of the urface of wall in particular variant It may eem futile to analyze relationhip between the conumption of material and the building cubic capacity, having examined the it relation to the footprint. And actually many deigner will think o. However, we hould know that the cubic capacity of a building may change depending on a variety of parameter. The 332
implet one, uually temming from the applied technology, are the footprint at the contant height of aile, variable height at the contant floor area and changeable dimenion of a hall only at certain point long- or idewie. The analyzed model are imple hall, which i why the quetion of the unification of element will not be conidered. We will dicu, however, the effect of the urface of encaement to thee cot of ued material per tructure, provided the ame ytem of building the wall. All that need to be done i to compare frame of the pan preented before to the lateral urface alone, and owing to their proportional increae a the length of the hall increae, they can be analyzed in the ame way a for a ingle-pan hall. The total cot of encaing the building will decreae proportionally to the decreaing cubic capacity of the hall, which mean the decreaing ize of vertical urface. However, let u focu on the analyzed variant, which we compare with repect to their unit encaement urface. It hould be added that the total urface i different for each variant due to the changing width of pan. In uch comparion, a in the above point, the reinforced concrete tructure i the mot economical olution in term of the conumption of material. Comparing hall with the ame cubic capacity and footprint, and conequently with the ame cot of building outide wall, building object raied from teel will be a more expenive variant with repect to the cot of material (Pawłowicz et al.2011). 4.2. Time of contruction work Another important criterion helping to chooe the bet olution i the time it will take to contruct a given building. Each day at a contruction ite incur huge cot, due to the labour done by people and machine. The preented analyi i baed on generally accepted time tandard determined according to the current behaviour on the market. When conducting uch analyi, it i adviable to pay attention technologie employed in order to execute the analyzed variant. A aumed before, the reinforced concrete frame will be made on the ite, a monolithic tructure, while the teel one will be raied from prefabricated element made in a factory. The work required to make ferroconcrete frame include: reinforcement with teel rod (main, tranvere and additional reinforcement), making pole caffold and formwork under the pandrel beam, curing of concrete. We hould alo add the time needed to make cement, but in the cae analyzed herein we aumed that ready-made cement will be delivered from a cement plant (Szafranko 1997). Reinforced concrete contruction Fig. 5. Comparion of the time needed to build a ferroconcrete and teel tructure in particular variant The work which mut be included in an analyi of a teel tructure aembled at the beginning are the aembly of element delivered from a plant and covered with priming paint, and then painting the whole tructure on the contruction ite. A quick look will be enough to ee how much the two technologie differ from each other, 333
although they are ued to erect eemingly imilar building object. The monolithic tructure involve much more complicated work, trongly dependent on numerou external condition, which ha an evident influence on the eventual duration of contruction work. The diagram illutrate difference in the time it take to produce one frame in either of the two variant. The number correponding to working hour needed to make element of the building object ocillate within 53 to 277, which mean that the work time extent by 32-50 hour for each 2-meter increae of the frame pan. Eventually, the change of the pan between the column reaching the maximum planned ditance caue an increae in the duration of the contruction work by a much a 80%. The increaing tendencie are imilar in character for both analyzed technologie, and the teel contruction i obviouly much better than the reinforced concrete one, which take much longer to make. 4.3. Reitance of contruction to corroion and fire Another iue that need to be conidered i the reitance of a contruction to unfavourable environmental condition, ubtance cauing corroion and high temperature that occur during a fire. Typically, building tandard help u claify individual element and decribe the characteritic they hould demontrate under uch circumtance (González et al.1995). All contruction hould be a fireproof a poible, which mean they hould retain their function during a fire. The recommendation contained in the national guideline aim at preerving the tability of whole contruction a well a their element for a et time depending on their cla. Another aim i to enure that further preading of a fire or moke, a well a a rik of ignition will be controlled, and the contruction will behave in a way that will enable and facilitate fie recue and ecape action. Thee condition are conidered in the context of material ued for making whole contruction or their contituent part, and their interaction during a fire. The two analyzed model contruction belong to non-flammable material with low moke emiion. Claification of element depend on two apect: the criteria and the time during which thee criteria mut be met. The claification of each element mut be determined during the deign tage o a to enviage way of additional, external fire control. The main reaon why thi i o important to analyze tolerance of contruction to fire i that under high temperature material automatically loe reitance. Steel ha many advantageou characteritic, but i very enitive to high temperature. All teel contruction are typically given fireproof protection, without which they will not lat longer than half an hour. The problem i le eriou in the cae of reinforced concrete tructure, but cannot be neglected altogether. Reinforced concrete contain teel element, which perform an important function in the behaviour of ferroconcrete contruction. When it come to protection of ferroconcrete tructure, the olution i imple. In order to provide all element with a deired fireproof cla, minimum dimenion of cro-ection and an adequate thickne of concrete cover for the reinforcement are deigned. Thi i uually the only and ufficient method to protect newly raied contruction. Sometime, however, dimenion of particular element are limited by technological or architectural demand, which i when other method mut be deployed. Thee mot frequently are: thick-layer cover uch a fireclay mortar prayed directly over the contruction, analogouly to teel tructure. Other ytem applied to teel contruction are not uitable to protect ferroconcrete tructure from fire (Bentz, Collin 2004). Reitance to corroion i different for different material, and therefore there are different anti-corroion olution. Regarding teel, which i ued in both ytem, corroion i caued by formation of different alt on the urface of a teel element due to reaction of element from the metal with other element. Anti-corroion method include prevention of moiture and water collection by giving appropriate hape to the element and whole tructure, or by reducing their emiion when uing the building, or by avoiding direct contact between unprotected teel with material having different electro-chemical potential, e.g. aluminum. However, by being o vulnerable to the effect of external condition, thi material need additional protective action. They include two baic form: paint layer and galvanizing. Thee are unneceary in ferroconcrete contruction becaue the concrete itelf function a a protective cover. Attention hould be paid, however, to the width of gap and thickne of concrete cover, which are regulated by norm and depend on the environment. According to the European norm, expoition clae are repreented by the letter X and, depending on the environment, the number 0 when corroion rik i abent, C damage caued by carbonization, D corroion due to chloride, S effect of chloride from eawater, F element expoed to cyclic freezing and thawing, and A under chemical effect. Layer of concrete cover alo depend on the cla of applied cement and the number of check carried out. The quetion of cratche i uually olved during the deigning tage, by electing adequate cro-ection of element and amount of reinforcement. 334
Conidering the above information, it can be concluded that anti-corroive protection i imilar to the way of enuring tolerance to high temperature. Thu, teel contruction require ue of different protection ytem, while corroion of ferroconcrete tructure i prevented at the deign tage by providing ufficiently thick concrete cover. Becaue the fireproof and anti-corroive coating on teel component can be combined, they were not analyzed eparately, becaue the cot of painting teel urface would be imilar. On the other hand, in our analyi of monolithic tructure, the thickne of concrete cover wa conidered imultaneouly regarding the unfavourable influence of the urrounding and an event of a fire. 4.4. Ue of the contruction The major financial outlay which an invetor mut incur during the contruction proce hould be amended by adding the cot needed to ue and maintain a ready building object. Beide typical cot caued by maintenance, on a more or le ame level each year, the analyzed model tructure need periodic check and repair (Wei- Wen, Winter. 1960). Fig. 8. Cot of renovating one teel and ferroconcrete frame after 10 year, for each of the pan variant; The diagram in figure 8 how difference in cot of renovation of the model olution. With maller pan, thee cot are imilar in both type of contruction, but a the pan increae, the difference reache 42%. In each variant, the financial input on renovation are higher in the cae of a teel tructure, and differ by 6% to 42% from analogou reinforced contruction. Regarding both type of olution in the variant with the maximum tranvere pan of column, the difference rie by 81% and 69%, repectively. It i alo poible to refer the calculated value to 1 m 2 of renovated urface. Thee data are included in the table 2, below. 335
Tab. 2. Specification of cot of renovating 1 m 2 of teel and ferroconcrete contruction No of variant Total cot of renovation [PLN] Steel contruction Area ubmitted to renovation [m 2 ] Cot of renovation of 1m 2 [PLN] Total cot of renovation [PLN] Ferroconcrete contruction Area ubmitted to renovation [m 2 ] 1 486,12 15,38 31,60 456,37 20,45 2 695,33 20,10 34,59 571,30 25,61 3 911,76 24,35 37,45 658,86 29,53 4 1254,50 30,54 41,08 823,54 36,91 5 1721,24 38,93 44,21 973,17 43,62 6 2087,48 44,96 46,43 1238,42 55,50 7 2548,46 51,89 49,11 1479,61 66,31 Cot of renovation of 1m 2 [PLN] 22,31 The data contained in the table verify the commonly accepted claim that reinforced concrete contruction are much more durable and under normal exploitation condition do not require any major repair during the planned uability life. 4.5. Cot of making the contruction The total cot of contruction conit of variou component. Out of the one dicued above, the given pecification contain cot of erecting the contruction, cot of renovation and maintenance and cot of anticorroive and fireproof protection. - renovation - corroion protection - equipment - additional material - labour - the bae material [variant nr] Fig. 9. Contribution of particular cot of building and uing a a ingle ferroconcrete frame in particular pan ize variant 336
In ferroconcrete contruction, the highet hare to the total cot i contributed by the main contruction material and labour thee cot are imilar in all variant. The protection of a contruction againt corroion or fire i minimal, almot negligible, which implie that it i very hardy to external environmental factor. - renovation - corroion protection - equipment - additional material - labour [variant nr] Fig. 10. Share of individual type of cot of building and uing a ingle teel frame in particular pan ize variant Fig.10 how a very high hare of baic contruction material in the total cot of erecting and maintaining a teel tructure. Steel a a building material i very expenive. Alo, notable i a higher percentage of cot of renovation and protection than in the cae of ferroconcrete contruction. The other cot component are imilar in both cae and do not increae notably a the pan increae. Fig. 11. Total cot of building and uing a ferroconcrete frame and a teel frame relative to one frame in each variant The diagram in fig. 11 confirm our previou obervation. Having analyzed all the variant, we can conclude that ferroconcrete contruction are a much more economical olution. Although the difference are mall for contruction with maller pan, it would be uneconomical to chooe a teel contruction when the pan between column i 18 m, a thi olution i 70% more expenive. 337
Tab. 3. Main advantage and diadvantage of teel and ferroconcrete contruction advantage Ferroconcrete contruction -low cot of making and maintaining -mall error while building are reparable at relatively low cot, diadvantage -long time to build, -the multi-component element enitive to change in loading direction, -large deviation of dimenion of element, -difficulty in reproducing deign aumption, -much labour input to build, -many factor calling for care and attention on a contruction ite, -cotly reinforcement of the contruction, the contruction cannot be diaembled, -the material i practically unrecoverable, -large weight of the whole contruction, -cro-ection of element diminih the uable floor urface and cubic capacity, -difficultie during the aembly of intallation inide the building. diadvantage Steel contruction -high cot of making and maintenance, -each, even the mallet mitake caue eriou conequence, advantage -relatively hort time to build, -the iotropic material reitant to change in loading direction, -mall deviation in dimenion of element, -eae of reproducing deign aumption, -few activitie that require control on a contruction ite, -quite imple and inexpenive way to reinforce the contruction, -poible diaembly of the contruction, -the material can be recovered, -relatively light contruction, - cro-ection of element need not decreae the uable floor area or cubic capacity, -eay to aemble intallation in the building. 5. CONCLUSIONS In the civil engineering practice, there are many way of completing contruction invetment project. Each contruction can be built in a number of way, which enable architect and deigner to prepare different variant of planned building. The requirement et in front of building contruction, decribed above, how how wide i the range of analye concerning the dicued olution. The model contruction can be made a a teel or monolithic ferroconcrete tructure. The decription of the contruction given in thi article demontrate how differently the individual criteria are atified by the two technological variant. The table 3 juxtapoe other apect, which cannot be compared otherwie, for example a diagram, becaue they are not mathematically comparable. The red colour highlight advantage. REFERENCES Ajdukiewicz A.(2011). Apekty trwałości i wpływu na środowiko w projektowaniu kontrukcji betonowych. Przegląd Budowlany 5/2011. Bentz E. C, Collin M. P. (2004). Development of the 2004 Canadian Standard Aociation (CSA) A23.3 hear proviion for reinforced concrete. Canadian Journal of Civil Engineering 33 (5) Dąbrowki K., Stachurki W., Zielińki J.L. (1982). Kontrukcje betonow.. Wydawnictwo Arkady, Warzawa. 1982. 338
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