TENSILE MEMBRANE STRUCTURE FORCES DEPENDENCE ON DIFFERENT PARAMETERS UNDER POINT LOAD ACTION

Zategnute membranske konstrukcije trenutno su tema mnogih istraživanja. Iako njihovo projektovanje još uvek nije standardizovano na nivou Evrope, publikovane su Smernice za projektovanje [5] i Nacrt evropskog pravilnika [17]. Postoji mnogo povoljnih karakteristika membranskih konstrukcija, pre svega, njihova mala sopstvena težina, njihove atraktivne forme i veliki rasponi. Uz to, poznata su i njihova nepovoljna svojstva. Zbog svojih termičkih karakteristika, one se češće koriste za natkrivanje nego za zatvaranje prostora. Upravo ova tema trenutno je aktuelna u istraživanjima [4,8,10]. Ipak, postoji i puno aspekata membranskih konstrukcija koji još uvek nisu dovoljno istraženi. Efekti dejstva koncentrisanih sila za sada nisu potpuno razjašnjeni. Ovaj rad prikazuje istraživanje koje se bavi ispitivanjem uticaja koncentrisanih sila na sile zatezanja u membrani. Koncentrisane sile u proračunu najčešće predstavljaju dejstvo ljudi koji stoje na membrani, što se obično dešava pri održavanju membrane. Sile zatezanja su ključne u proračunu membranskih konstrukcija. Na osnovu maksimalnih sila zatezanja, određuje se odgovarajući membranski materijal za svaku konstrukciju. Zbog


INTRODUCTION
Tensile membrane structures are subject of many ongoing researches. On the European level, they are still not codified; however, the Design Guide [5] and Prospect for European Guidance for the Structural Design [17] are published. There are many advantageous properties of tensile membrane structures, most notably their low self-weight, attractive forms, and large spans. Additionally, some of their negative aspects are also known. Thermal properties of tensile membrane structures are the main reason why they are preferably used to cover open spaces instead of enclosing them. This is one of the most interesting research areas in the field of tensile membrane structures [4,8,10]. However, there are also some aspects of tensile membranes which are still insufficiently explored. The effects of point load actions on tensile membrane structures are currently incompletely clarified. This paper presents research that deals with the impact of point load actions on changes of membrane forces. Point load actions are mostly induced by persons standing o n the membrane. This usually happens during the maintenance of the structure. On the strukture membranskog materijala, sile zatezanja definišu se u dva pravca -glavnom i pomoćnom, tako da prate pravce vlakana tkanog membranskog materijala.
Svi modeli imaju kvadratnu osnovu, sa stranicom dužine 6 m. Modeli su sedlastog oblika, sa po dva viša i po dva niža oslonca. Ivični oslonci su pravi i nepomerljivi. Karakteristike membranskog materijala other hand, membrane forces are fundamental during the structural analysis of tensile structures. Based on the values of maximum tensile force, the appropriate membrane material is selected for each analyzed structure. Due to the membrane material structure, membrane forces are analyzed in two directions, warp and weft, following the yarns of the woven fabric.
There are few researches investigating point load actions on tensile membrane structures or the membrane forces of tensile membranes. However, Huntington states that point loads should be taken into account in the structural analysis of tensile membrane structures [9]. It is known that point load actions cause large deflections and changes in tensile membrane forces [12]. There is a research exploring the deflections of a rubber membrane under point load [15]. Valdes, Miguel and Onate test the proposed analysis methodology on flat membrane under point load [20]. Deflections of membrane structures under point load depending on several parameters are also investigated [13,14]. Bridgens, Gosling and Birchall investigate membrane material behaviour and show warp and weft stresses under biaxial testing [2,3]. Gosling and Bridgens proposed a new approach for fabric stressstrain behaviour representation [6]. Bridgens and Birchall present results for membrane forces under snow and wind loading [1]. Gosling et al. also provide data for membrane forces under the same loads as a part of their research [7].
This paper presents research done on the dependence of membrane forces on different parameters. It builds on the previously published paper [11] by adding one more variable parameter into consideration. Variable parameters are the height of the model, the intensity of prestressing forces, and t he orientation of the membrane material. The goal of the research is to make a step towards better understanding the effects of point load actions and finding out which types of tensile membrane structures are more susceptible to point load actions. Additionally, this research aims to investigate the importance of the point load actions for tensile membrane structures. It will be done by comparing maximal membrane forces under point and another common load at different sets of variable parameters. Wind and snow loads act commonly on tensile membrane structures. Seismic loads are insignificant because of the lightweight nature of membranes; however, if the structure incorporates some heavy parts, a seismic analysis should be conducted [5,21]. Therefore, due t o the dynamic nature of wind actions, snow load was selected for comparison with point load action as the least complex.

METHODOLOGY
Research for this paper is conducted on models of tensile membrane structures which are formed in software Sofistik [16]. This software was already used in scientific researches, for example, in the doctoral thesis [13,18,19]. Some model parameters are fixed for all models, while others are varied in order to investigate their influence on membrane force intensities.

Raspored sila zatezanja
Nakon izvršenog proračuna svih modela, usledila je analiza rezultata. Primećeni su određeni obrasci ponašanja kada je u pitanju raspored intenziteta sila zatezanja u membrani. Jedan karakterističan primer prikazan je na slici 2. Na toj slici prikazani su rezultati za model koji ima visinu 2 m, intenzitet prednaprezanja 3 kN/m i paralelnu orijentaciju materijala. Slika prikazuje vrednosti intenziteta sila zatezanja u glavnom i pomoćnom pravcu, i od dejstva koncentrisane sile i od dejstva snega. Kao što je i bilo očekivano, maksimalna sila zatezanja, pod dejstvom koncentrisane sile, zabeležena je na mestu dejstva opterećenja, odnosno u centru membrane. U glavnom pravcu područje sila zatezanja s višim intenzitetom proteže se duž vlakana glavnog pravca prema ivicama membrane. Najveći deo membrane trpi samo male promene u intenzitetima sila zatezanja. Na manjem delu membrane dolazi do smanjenja intenziteta sila zatezanja. Slično se događa i same direction as the diagonals of the base. Both of these orientations are analyzed in this research. Changing the height of the models with the same base directly affects the curvature of the model. The higher the model, the greater the curvature is. For the 6x6 m base, in this research, the height of the models is varied from 1 to 3 m. These values are selected as the most realistic for the given base dimension. The analyzed values of the model height are 1.0, 1.5, 2.0, 2.5, and 3.0 m. Prestressing the membrane will help it resist external loads more efficiently. The intensity of the prestress is defined separately in warp and weft direction, but in this research, these values are taken to be the same. The range of prestressing values from 1 to 5 kN/m covers the most frequently used prestress intensities. Therefore, in this research, values of 1, 2, 3, 4, and 5 kN/m are selected for analysis. Figure 1 shows the variations of membrane orientation and model height. The change of prestressing intensity is not shown since it does not affect the appearance of the membrane.
There are two variations in material orientation, five different values for the height of the models, and five different values for the prestress intensities. This makes a total of 50 different models that will be analyzed. Each of the models will be loaded, and resulting maximal membrane forces will be monitored. The third-order theory is used in the analysis. Software Sofistik uses a modified force density method for the calculation of membrane structures.

RESULTS AND DISCUSSION
The research is divided into three parts. In the first part layout of the membrane forces under point load is investigated. Changes of membrane forces are monitored and described. The second part of the research analyzes the parameters that influence changes of membrane forces. The obtained results can be used for reducing maximal membrane forces under point load. The third part of the research investigates the importance of point load actions to tensile membrane structures. Resulting maximal membrane forces from point load action will be compared to the results under snow load.

Force intensities layout
After the calculation has been carried out on all models, the results were analyzed. Specific patterns of behaviour are noted regarding the layout of membrane force intensities. One typical example is shown in Figure  2. In this figure, the results from a model with the 2 m height, prestress intensity of 3 kN/m, and parallel membrane orientation are presented. The figure presents membrane forces in both warp and weft direction, from point load and snow load. As expected, maximal membrane forces under point load in both directions occur in the position of the point load, i.e. in the centre of the membrane. Area of higher membrane forces in warp extends along the direction of warp yarns towards the edge supports. The largest part of the membrane suffers only small changes in membrane force. A smaller part of the membrane will experience a reduction of membrane forces. A similar situation is in u pomoćnom pravcu, gde oblast s većim intenzitetom sila prati vlakna pomoćnog pravca, počevši od centra membrane. Zapravo, rasporedi intenziteta sila zatezanja u glavnom i u pomoćnom pravcu ogledalski su preslikani sa osom simetrije koja prolazi kroz dva niža ili dva viša oslonca. Nasuprot ugibima, koji su pod dejstvom snega najveći u centru membrane, sile zatezanja su najviše blizu ivičnih oslonaca. Najniže sile zatezanja zabeležene su u nižim osloncima. Rasporedi intenziteta sila pod dejstvom snega u glavnom i pomoćnom pravcu takođe su simetrični po dijagonalama. the weft direction, where higher membrane forces follow the direction of weft yarns, starting from the centre. Actually, the layout of forces in weft and the layout in warp direction are mirrored along the axis defined by either two low points or two high points. In contrast to deflections where maximal deflections are recorded in the centre, the snow load produces maximal membrane forces close to the edge supports. Minimal forces occur at low points. The layout of membrane forces under snow load in warp and weft are also mirrored along diagonals. Slika 3 prikazuje rezultate za model s visinom od 2 m, intenzitetom prednaprezanja 3 kN/m i dijagonalnom orijentacijom materijala. Jedina razlika u poređenju s modelom prikazanim na slici 2 jeste u orijentaciji materijala. Ipak, rezultati kod ovih modela uočljivo su drugačiji, i u pogledu intenziteta sila zatezanja i prema njihovom rasporedu. U odeljku 3.2 biće detaljnije razmatrani intenziteti sila, dok se ovaj deo bavi samo njihovim rasporedom. Pri dejstvu koncentrisane sile, maksimalne sile Figure 3 shows the results from the model with 2 m height, prestress intensity of 3 kN/m, and diagonal patterning. The only difference compared to the model in Figure 2 is in membrane material orientation. However, the results differ significantly, both in the intensity of membrane forces and in their layout. Chapter 3.2 will discuss the maximal intensity of membrane forces in more detail, while here, only the layout of forces will be discussed. Under point load, maximal membrane forces zatezanja u glavnom pravcu zabeležene su na mestu dejstva opterećenja, odnosno u centru membrane. Visoki intenziteti sila zatezanja koncentrisani su oko ove tačke. Međutim, u pomoćnom pravcu, maksimalne sile primećene su ili u centru membrane ili kod ivica membrane blizu viših oslonaca. Kod viših intenziteta prednaprezanja i viših modela, maksimalne sila zatezanja u pomoćnom pravcu nisu se nalazile u centru membrane. Ovo se objašnjava većom sposobnošću membrane da se odupre dejstvu koncentrisane sile u centralnom delu bilo zbog veće zakrivljenosti, zbog povećanog intenziteta prednaprezanja ili zbog kombinacije ovih faktora. Niži intenziteti sila zatezanja nalaze se blizu nižih oslonaca, a u nekim slučajevima u centru membrane. Raspored sila zatezanja u pomoćnom pravcu skoro se potpuno razlikuje u odnosu na model s paralelnom orijentacijom materijala. U glavnom pravcu, oblast membrane s višim silama zatezanja pruža se duž glavnih vlakana prema višim osloncima. Veći deo membrane ima male promene intenziteta sile zatezanja. Raspored intenziteta sila zatezanja sličan je modelu s paralelnom orijentacijom materijala, budući da područje visokih intenziteta sile zatezanja prati glavna vlakna, s tim što su vlakna drugačije orijentisana. Pod dejstvom opterećenja od snega, u glavnom pravcu, najveće sile zatezanja nalaze se u centralnom delu membrane i ka višim osloncima. Treba napomenuti i to da su ponovo visoki intenziteti sila zatezanja raspoređeni duž vlakana pravca koji se razmatra. Najniže sile zatezanja postoje kod nižih oslonaca. Raspored intenziteta je u pomoćnom pravcu obrnut. Oblast s nižim intenzitetom sila zatezanja proteže se od centralnog dela membrane k nižim osloncima. Maksimalne sile zatezanja nalaze se blizu viših oslonaca.
Prvi zaključak u vezi s rezultatima predstavljenim na slici 4 jeste da su maksimalne sile zatezanja pod dejstvom koncentrisane sile iste i u glavnom i u pomoćnom pravcu. Ovakvo ponašanje objašnjava se dvostrukom simetrijom membrane. U slučaju paralelne orijentacije materijala, vlakna glavnog i pomoćnog pravca iste su dužine i jednako su opterećena, te su sile zatezanja iste. Sledeći zaključak jeste da je uticaj dva analizirana parametra na sile zatezanja potpuno različit. Može se primetiti da visina modela praktično ne utiče na vrednost maksimalnih sila zatezanja. Ovo je veoma zanimljivo, jer se smatra da je povećanje visine modela, odnosno povećanje zakrivljenosti modela, način da se smanje negativni uticaji spoljašnjeg opterećenja. Međutim, u slučaju paralelne orijentacije materijala, vlakna nisu zakrivljena iako je model zakrivljen, budući da se forma modela može generisati s dva seta pravih linija. Stoga, povećanje visine modela ne utiče na in warp occur at the position of point load, in the centre of the membrane. High intensities are concentrated around this point. However, in weft direction maximal forces occur either in the centre of the membrane or at the edge supports close to high points. At higher prestress intensities and larger height of the models, maximal forces in weft are unlikely to occur at the centre. This is explained by the increased capacity of the membrane under the position of point load to resist loading either by increased curvature, increased prestress forces, or both. Lower membrane forces exist in the areas close to the low supports and, in some cases, in the centre of the membrane. The layout of forces in the weft direction is almost completely different compared to the model with parallel orientation. In warp direction, the area of higher forces spreads along the direction of warp yarns towards the high supports. Most of the membrane has small changes in membrane forces. This layout is similar to the one on the model with parallel orientation since the areas of high membrane forces are aligned with the warp yarns, only the yarns are differently oriented. Under snow load in the warp direction, high membrane forces are located in the central part of the membrane and towards the high supports. It can be noted that, once again, the arrangement of high forces follows the direction of the analyzed yarns. Lowest membrane forces are present at low supports. In weft direction, the layout is quite the opposite. The area of low membrane forces stretches in the central part of the membrane and towards the low supports. Maximal membrane forces are present close to high supports.

Change of force intensities
This chapter shows the results for all 50 analyzed models under point load action. First, the results for models with parallel membrane material orientation are presented. The intensity of the prestress and the height of the models were varied in the selected range. Maximal membrane forces of these models are shown in Figure 4. The graphs in this figure show the results for warp and weft direction separately. In the same manner, the results of models with diagonal patterning are given in Figure 5.
The first conclusion about the results presented in Figure 4 is that the maximal membrane forces under point load in warp and weft directions are the same. This behaviour is explained by double symmetry of the membrane. In the case of parallel membrane material orientation, the yarns of warp and weft have the same length and are evenly loaded, thus the resulting membrane forces are the same. The next conclusion is that the impact of the two analyzed parameters on maximal membrane forces is much different. It can be noticed that the height of the models practically does not affect the value of the maximal membrane force. This is very interesting since increasing the height of the model, i.e. increasing the curvature of the models, is often used as a method for reducing the negative effects of external loads. However, in the case of parallel patterning, yarns lack curvature, although the model is double curved since the form of the model can be generated with sets zakrivljenost vlakana, te ostaju prava, ako zanemarimo nabore nastale tkanjem vlakana. S druge strane, povećanje intenziteta prednaprezanja dovodi do povećanja maksimalnih sila zatezanja. Ova veza je nelinearna. Promena maksimalnih sila zatezanja u slučaju svih modela pod dejstvom koncentrisane sile najveća je pri intenzitetu prednaprezanja od 1 kN/m, a opada s povećanjem intenziteta prednaprezanja. Minimalne sile zatezanja pod dejstvom koncentrisane sile nisu istraživane u ovom radu. of straight lines. Therefore, the increase of models' height does not affect the curvature of the yarns and they remain straight if we disregard crimp. On the other hand, the increase of the prestress intensity will lead to an increase in maximal membrane forces. This relation is nonlinear. The change of maximal membrane force for all model heights, under point load, is the largest at models with the prestress intensity of 1 kN/m and this change decreases as the prestress intensity increases. Minimal forces under point load are not investigated in this research.

Figure 4. Maximal membrane forces of models with parallel patterning under different prestress intensity and model height, in warp (above) and weft (below)
Rezultati prikazani na slici 5 prikazuju različito ponašanje membrana s dijagonalnom orijentacijom materijala, u odnosu na one s paralelnom orijentacijom. Pre svega, rezultati u glavnom i u pomoćnom pravcu nisu isti. Razlog za to jeste suprotna zakrivljenost vlakana glavnog i pomoćnog pravca kod dijagonalne orijentacije materijala. Zbog toga, opterećenja koja deluju vertikalno naniže nemaju isti uticaj na njih. U glavnom pravcu, oba analizirana parametra značajna su The results presented in Figure 5 show different behaviour of membranes with diagonal orientation, compared to parallel orientation. The results in warp and weft direction are different. The reason for this lies in the fact that warp and weft yarns have opposite curvature in models with diagonal patterning. Therefore, vertical downward loads do not have the same impact on them. In the warp direction, both of the analyzed parameters influence the maximal membrane forces. Increase of za vrednost maksimalnih sila zatezanja. Povećanje visine modela rezultira povećanjem maksimalne sile zatezanja. Povećanje intenziteta prednaprezanja ima kompleksnije dejstvo. Prilikom povećanja intenziteta prednaprezanja, sile zatezanja najpre opadaju, a zatim rastu. Ovakvo ponašanje detaljno je objašnjeno u prethodnom istraživanju [11]. Sila zatezanja pod dejstvom opterećenja jednaka je zbiru sile prednaprezanja i promene vrednosti sile izazvane dejstvom opterećenja. Na analiziranim modelima, promena vrednosti intenziteta sile smanjuje se s povećanjem intenziteta sile prednaprezanja, dajući sumu prikazanu na slici 5. U pomoćnom pravcu, intenzitet prednaprezanja ima veći uticaj na sile zatezanja u poređenju s visinom modela. Povećanje intenziteta prednaprezanja rezultuje povećanjem maksimalnih sila zatezanja. Visina modela ima značajniji uticaj na maksimalne sile zatezanja u pomoćnom pravcu kada su u pitanju modeli s nižim intenzitetom prednaprezanja, a taj uticaj opada s povećanjem prednaprezanja. model height results in an increase in the maximal membrane force. The increase in the intensity of prestressing has a more complex impact. When increasing the intensity of prestressing membrane forces start declining at first, but afterward, it starts to increase. This phenomenon is explained in detail in previous research [11]. Membrane force under load equals prestressing force plus the change of membrane force due to loading. On the analyzed models, the change of membrane forces decreases as the prestress forces increase, giving the sum as presented in Figure 5. In the weft direction, the intensity of prestressing has a greater impact on membrane forces than the height of the model. The increase of prestressing intensity results in an increase in maximal membrane forces. The height of the model has a more significant influence on the maximal membrane forces in weft for models with lower prestress intensity, and it decreases as the prestress increases.
Treba napomenuti i to da među modelima s dijagonalnom orijentacijom ima puno negativnih vrednosti. U glavnom pravcu od analiziranih 25 modela postoji 16, a u pomoćnom pravcu od 25 modela postoji 11 kod kojih koncentrisana sila dovodi do većih sila zatezanja nego opterećenje od snega. Ukupno, postoji devet modela kod kojih koncentrisana sila proizvodi veće Maximal membrane force intensities among models with parallel and diagonal patterning were also compared. Models with parallel patterning have maximal force intensities in warp direction from 3.72 to 5.85 kN/m. Maximal membrane forces of m odels with diagonal patterning are from 6.38 to 8.01 kN/m. This means that models with diagonal patterning have larger maximal membrane forces in the warp direction. In weft direction, membrane forces of models with parallel patterning are the same as in w arp, and membrane forces of models with diagonal patterning range from 1.67 to 5.46 kN/m. It should be noted that all models with diagonal patterning have smaller membrane forces in weft direction compared to models with parallel patterning.

Comparison of force intensities under point and snow load
The layout of force intensities and change of force intensities were analyzed in two previous chapters. However, the importance of values of membrane forces under point load was not discussed. This part of the research is dedicated to exploring the significance of point load actions to membrane forces of tensile membrane structures. In order to check the importance of point load effects, they were compared to the effects of snow load. The intensity of 1 kN f or point load, representing one man, and the typical intensity of 0.6 kN/m 2 for snow load were selected for analysis. These load intensities simulate common loads acting on membrane structures and thus provide comparable results. Figure 6 presents the results of the comparison of snow load and point load effects to membrane forces for models with parallel patterning. Maximal membrane forces under point load were deducted from corresponding membrane forces under snow load. Practically, negative results would show that membrane forces are larger under point load than under snow load. Among models with parallel membrane material orientation, there are no such cases. In most cases, membrane forces are significantly larger under snow load. The difference in membrane forces under snow and point load decreases with the increase of height of the model and is the smallest for the model with the lowest prestress value. Figure 7 presents the results for the models with the diagonal orientation of membrane material in the same way as Figure 6. Results in Figure 7 show that differences are dependent on both the height of the model and the prestress intensity. In warp direction value of differences decreases as the height of the models increases. In addition, it decreases with the decrease of the prestress intensity. In the weft direction value of differences also decreases when the prestress intensity is lowered. However, the increase of model height will not lead to an unambiguous change of differences.
It can be noted that among models with diagonal orientation, there are many cases with negative values. In warp there are 16 models out of 25 and in weft 11 out of 25 models in which point load produces larger membrane forces than the snow load. Overall, there are 9 models in which point load produces larger membrane sile zatezanja i u glavnom i u pomoćnom pravcu, u poređenju sa opterećenjem od snega. Najveća razlika između sila zatezanja izazvanih koncentrisanom silom i opterećenjem od snega zabeležena je u glavnom pravcu kod modela sa intenzitetom prednaprezanja 1 kN/m i s visinom od 3 m. Ova razlika iznosi 3,47 kN/m u korist koncentrisane sile. Ovaj rezultat je značajan jer dokazuje relevantnost dejstva koncentrisanih sila na membranske konstrukcije.
forces in both warp and weft directions compared to snow load. The largest difference between point and snow load is recorded in warp direction in model with 1 kN/m prestress value and 3 m height. This difference has a value of 3.47 kN/m and is in favour of point load. This finding is very important and proves the significance of point load actions to tensile membrane structures.

CONCLUSION
In this research, different models of tensile membrane structures were tested for the effects of 1 kN point load acting in the centre of the membrane on membrane forces. All model parameters except the orientation of the membrane material, the intensity of the prestressing force and the model height were kept constant. By changing these parameters, 50 models were created. All models were loaded with the same point load and also 0.6 kN/m 2 snow load that is used for comparison.
The second part of the presented research aimed at investigating the influence of varied parameters on maximal membrane forces. The results showed that the change of model height does not affect maximal membrane forces if the orientation of material is parallel. The increase of prestressing intensity causes the increase of maximal membrane forces at models with parallel patterning. Models with diagonal patterning in warp direction have relatively small changes of maximal membrane forces when the height of the model and prestress intensity are varied. The increase of model height leads to an increase of maximal membrane forces in the warp. In weft direction increase of prestressing intensity will result in a significant increase of maximal membrane forces. The height of the model has a larger influence at lower prestress intensities.
In the last part of the research, maximal membrane forces under point load are compared to maximal membrane forces under typical snow load. This was motivated by the need to evaluate the significance of changes in maximal membrane forces under point load. Models with the same properties, except the orientation of the material, will have larger maximal forces in the warp and lower maximal forces in weft in case of diagonal patterning under point load. However, when compared to membrane forces under snow load, all models with parallel patterning have lower membrane forces caused by point load. Among models with diagonal patterning, nine models have larger membrane forces in both warp and weft compared to snow load. This shows that under certain sets of parameters, point loads can have a more significant impact on membrane forces than snow load.
The research presented in this paper deals with the topic that was not previously investigated in detail. Therefore, the presented findings should be used to further analyze the behaviour o f tensile membrane structures under point load actions. Conclusions obtained during this research should be verified by experimental testing on real tensile membrane structures. Further research will be directed towards the tensile membrane structures with flexible edges. The next phases of the research regarding the effects of point loads on tensile membrane structures will investigate minimal membrane forces and the possible loss of tension in the membrane.

Vuk MILOSEVIC Dragan KOSTIC Jelena MILOSEVIC
Point load actions may have a significant impact on deflections of tensile membrane structures. Research presented in this paper is aimed at exploring the effects of point load actions on membrane forces of tensile membrane structures. Therefore, three different parameters of the structure were varied, and the membrane forces resulting from point loads were monitored. Variable parameters are the height of the model, the intensity of prestressing forces, and the orientation of the membrane material. The research was done on models in specialized software. In order to evaluate the significance of point load effects, membrane forces were compared to those under snow load. The results of the research show the layout of membrane forces under point load and dependence of maximal membrane forces on the varied parameters. Specific sets of analyzed parameters lead to significant values of maximal membrane forces under point load action.