Semi Gantry Crane: When It’s the Right Structure and How to Specify It

A رافعة جسرية شبه is the most cost-effective indoor lifting upgrade available — but only when your site meets three specific structural conditions. For facilities that meet those conditions, it typically cuts civil construction cost by 25–40% compared with a full gantry crane covering the same working width. For facilities that don’t, specifying one anyway leads to either a failed structural assessment or an undersized crane that can’t handle the actual load cycle.

Most selection guides stop at “use a semi gantry crane when floor space is limited.” That framing is accurate but incomplete. The real question procurement teams face is whether their building structure qualifies, which configuration matches the duty cycle, and what documentation to request before signing a purchase order. This guide answers all three.

Voitto Crane supplies two semi gantry crane configurations: the BMH single-girder (2–16 t, $12,000–$40,000 market reference) and the BMG double-girder (5–320 t, $42,000–$70,000+). Both are referenced throughout with specifications taken directly from the Voitto product page.

Quick Reference: BMH vs BMG at a Glance

Source: Voitto Crane product specifications. Custom designs available — confirm final parameters with Voitto’s engineering team.

When a Semi Gantry Crane Is the Right Choice

The Building Has Structural Capacity on One Side Only

The semi gantry crane’s fundamental value proposition is this: it converts existing building infrastructure on one side into half the crane’s support system, so you only pay for the other half. One end carriage rides on a runway rail fixed to the building wall or column; the other rides on a single ground rail supported by one leg. The floor-level infrastructure requirement drops from two rail strips to one.

This matters most in three common facility types. First, older reinforced concrete buildings where one wall was designed to carry suspended loads but the opposite side was not and cannot easily be reinforced. Second, facilities where a column row exists on one side at the right height but the building’s opposite side is an open face, dock door, or curtain wall with no load-bearing capacity. Third, leased industrial buildings where the landlord has permitted use of one runway beam but structural modification of the full building is not permitted under the lease.

In each case, a full overhead crane requires structural work on both sides — often prohibitively expensive. A full gantry crane avoids the building structure entirely but requires two ground rails and two leg structures, consuming floor space on both sides. The semi gantry crane threads the needle: it uses what the building already provides and adds only what is strictly necessary on the ground.

The Application Requires a Second Hook Under an Existing Overhead Crane

Installing a semi gantry crane at a lower rail elevation beneath an already-operating overhead crane is one of the most underused capacity upgrades in fabrication and precast environments. Because the semi gantry girder height is below the existing overhead crane’s minimum hook height, both units can operate in the same bay simultaneously — effectively doubling available hooks with zero building modification.

The engineering constraint is headroom: the semi gantry girder must clear the existing crane’s minimum hook height by a safe structural margin (typically at least 300 mm plus any applicable national safe-clearance requirement). This must be confirmed by measurement before specifying lifting height, not estimated after the order is placed.

One Side of the Bay Must Stay Clear at Floor Level

When one side of a workshop bay needs to remain unobstructed — a loading dock, a vehicle aisle, a production conveyor, a site boundary — a full gantry crane becomes impractical because its leg and rail occupy floor space on both sides. An overhead crane avoids floor obstacles entirely, but requires runway capacity on both sides of the building. The semi gantry crane places one floor rail on the side where an obstruction is acceptable and uses the building structure on the clear side, leaving that floor completely open.

This is a frequent requirement in automotive and light manufacturing lines where one side of the bay doubles as a vehicle access lane during production hours.

When a Semi Gantry Crane Is Not the Right Choice

Most selection guides skip this section. Skipping it is where expensive specification errors begin.

The high-side building structure fails the load assessment. If a structural engineer confirms the building wall, column, or existing runway beam cannot carry the imposed rail load — both the vertical crane weight plus lifted load and the horizontal travel inertia forces — a semi gantry crane cannot be safely installed without first strengthening the building. In this scenario, a full gantry crane (self-supporting, no building dependency) is the correct alternative.

The application is outdoors with no building structure on either side. A semi gantry crane requires a building element on the high side. Open-yard, port, or outdoor storage applications belong in a full gantry crane specification.

Load or span requirements exceed BMG range. Voitto’s BMG covers to 320 t and 24 m span. Applications beyond these parameters require a dedicated engineering discussion — they do not fit within the standard semi gantry crane product range.

The facility layout changes frequently. A semi gantry crane is a fixed installation. If the production layout is expected to change materially within the equipment’s service life, that constraint should be raised with Voitto’s engineering team before specifying, since it may affect the value case.

How to Specify a Semi Gantry Crane: Four Steps

Step 1: Confirm the Building Can Carry the High-Side Rail Load

This is the only step that must happen before any crane parameters are finalised — not after. The elevated runway rail transfers two types of load into the building structure: vertical load (crane dead weight plus the full Safe Working Load, with dynamic factors applied per ISO 4301 or FEM 1.001) and horizontal load (crane travel inertia and lateral forces from off-centre lifts). Both must be within the building’s rated capacity.

To run the structural assessment, the engineer needs a preliminary load drawing from the crane supplier — specifically the maximum wheel load at the elevated rail, the distance between wheel contact points, and the crane travel speed. Request this drawing at enquiry stage, before the structural assessment is commissioned, not after. Trying to run the structural assessment without it produces an inconclusive result that has to be repeated once the crane parameters are confirmed.

If the assessment result is marginal, the practical options are: reinforce the building structure, specify a lower capacity unit whose wheel loads fall within the building’s rating, or switch to a full gantry crane. Attempting to proceed with a crane whose loads exceed the assessed building capacity is a compliance and safety failure regardless of how the crane is priced.

Step 2: Determine the Correct Duty Class

Duty class governs the design life of every drivetrain component — hoist motor, gearbox, drum, brake, wire rope — and selecting it correctly is the single factor with the largest impact on long-term reliability. Under FEM 1.001 and ISO 4301, duty class is set by two inputs: load spectrum class (how heavily loaded each lift is relative to SWL, on average) and total design life in number of lifting cycles.

The most common specification error is selecting duty class based on peak SWL while ignoring lift frequency. A crane lifting at 80–90% of SWL several hundred times per day needs a significantly higher duty class than a crane occasionally lifting near capacity for maintenance work, even if both have identical rated tonnage.

Use this as a practical starting reference:

Specifying A4 for an A6 application does not reduce cost in the long run. The gearbox and hoist components reach their design fatigue limits years ahead of schedule — and mid-service replacement of those assemblies typically costs more than the price difference between duty classes at purchase.

Step 3: Define Span, Lifting Height, and Hook Approach Dimensions

الامتداد is measured between runway rail centrelines — not between building walls. Verify the actual rail positions before specifying this parameter.

ارتفاع الرفع is the vertical distance from finished floor level to the maximum hook height under full load. Measure this against the highest required lift point in the facility (a machine installation height, a loading platform, or a mezzanine level), not the ceiling height. The gap between the hook and the crane girder soffit — the hook approach dimension — is consumed by the hoist body and is not part of the usable lifting height.

Hook approach on the leg side — the minimum horizontal distance from the crane leg centreline to the hook centre at maximum traverse — determines how close the crane can lift to the floor rail. If material must be set down close to the leg side wall or column, this dimension must be confirmed against the physical obstruction before the order is placed.

Step 4: Confirm Power Supply Voltage and Control Options

Voitto’s standard semi gantry cranes ship at 380 V / 50 Hz / 3-phase, which covers China, Europe, the Middle East, Southeast Asia, and most African markets. North American facilities (480 V / 60 Hz) and other non-standard supplies require custom electrical components; allow an additional 10–15 production days for these configurations.

Variable-frequency drive (VFD) control is available as an option on both BMH and BMG configurations. VFD provides smooth acceleration and controlled deceleration, which reduces mechanical shock on the drivetrain and improves hook positioning accuracy. For A5+ duty cycles or for applications where the hoist positions loads precisely — stamping presses, CNC machine loading, precast mould positioning — VFD is worth the upfront premium. For light workshop use at A4, it is optional.

آلان

أخصائي حلول الرافعات · رافعة Voitto

10+سنوات الخبرة.

5,000+الزبائن

50+الدول

متخصصون في حلول تصدير الرافعات العلوية، والرافعات الجسرية، والرافعات الجيبية، ورافعات الموانئ، ورافعات الجسور العلوية الكهربائية. خبرة تزيد عن 10 سنوات في مساعدة العملاء العالميين من خلال الاستشارات قبل البيع، واختيار السعة، والتكوينات الخاصة بكل موقع.

+86 136 3963 3287 [email protected] اتصل بنا

Certifications and Compliance

Certification requirements for a semi gantry crane are determined by the destination country and govern both import clearance and the buyer’s insurance and liability position. Confirm these before signing the purchase order — certificate gaps surface at customs or during the first insurance inspection, not before.

CE marking (EU Machinery Directive 2006/42/EC): Required for any lifting equipment placed on the market or put into service in the European Economic Area. The supplier must issue a signed EC Declaration of Conformity referencing the applicable harmonised standard for cranes. A logo on a datasheet is not a certificate. Request the original signed document and verify the crane model listed on it matches your order.

FEM 1.001 / ISO 4301 design compliance: These standards govern crane classification and design rules. The test certificate should confirm 125% overload testing was completed at the factory before shipment. Request this document explicitly — it is not always included in the default documentation package.

ISO 9001 quality management: Confirms the manufacturer operates under a documented quality system. Verify the certificate is current and that the scope of certification includes crane manufacturing — not just a parent company’s administrative operations.

EAC (TR CU 010/2011): Required for Russia, Kazakhstan, Belarus, and other EAEU member states. If this is the destination market, confirm EAC certification specifically for crane equipment before ordering.

OSHA 1910.179 (United States): OSHA compliance for overhead and gantry cranes is the responsibility of the site owner and the local installation contractor, not the manufacturer. Chinese suppliers cannot issue OSHA compliance certificates. Buyers in the US should confirm their local installer holds the relevant lifting equipment installation qualifications.

Request these documents at the enquiry stage, not after manufacture begins:

1. EC Declaration of Conformity (EU/EEA buyers) — verify the specific crane model is named
2. 125% overload test certificate with load and date
3. ISO 9001 certificate — current validity, crane manufacturing in scope
4. Structural steel mill certificates (S355 or equivalent)
5. Factory Acceptance Test (FAT) report with photos and load data

الخلاصة

A semi gantry crane is the right structure when the building can carry one runway rail, the span and capacity fall within the BMH or BMG range, and the floor-level layout benefits from a single-rail solution. It is the wrong structure when the building assessment fails, the application is fully outdoor, or the duty cycle exceeds the available configuration.

Three actions before you contact a supplier:

1. Commission the structural assessment on the high-side building element — request a preliminary load drawing from Voitto’s team first so the assessment uses real parameters.
2. Document your daily lift count and average loading pattern to confirm the correct duty class, not just the peak SWL.
3. Identify the certifications required for your destination market and request the full documentation list upfront.

Ready to confirm your specification? Contact Voitto Crane with your capacity, span, lifting height, and voltage — the engineering team responds within 24 hours.

آلان

أخصائي حلول الرافعات · رافعة Voitto

10+سنوات الخبرة.

5,000+الزبائن

50+الدول

متخصصون في حلول تصدير الرافعات العلوية، والرافعات الجسرية، والرافعات الجيبية، ورافعات الموانئ، ورافعات الجسور العلوية الكهربائية. خبرة تزيد عن 10 سنوات في مساعدة العملاء العالميين من خلال الاستشارات قبل البيع، واختيار السعة، والتكوينات الخاصة بكل موقع.

+86 136 3963 3287 [email protected] اتصل بنا

Author: Alan, Crane Solutions Specialist · Voitto Crane Last updated: 2026-09 · Recommended review cycle: every 12 months for pricing and standards updates Disclaimer: Final equipment selection must be confirmed by a certified engineer and comply with local lifting-equipment regulations.

الأسئلة الشائعة

Q1：What is the main difference between a semi gantry crane and a full gantry crane?

A semi gantry crane uses the existing building structure on one side — a wall, column, or existing runway rail — and adds a single ground leg and rail on the other. A full gantry crane is entirely self-supporting on two ground rails. The semi gantry is more cost-effective when suitable building infrastructure already exists on one side; the full gantry is the right choice for outdoor or greenfield sites with no building to attach to.

Q2：How do I know if my building can support a semi gantry crane?

You need a structural assessment from a qualified engineer before specifying. The assessment requires the crane’s maximum wheel load at the elevated rail — request a preliminary load drawing from Voitto Crane at enquiry stage so the engineer has real parameters to work with. Do not proceed to the order stage until this assessment is complete and confirms the building is rated for the imposed load.

Q3：What duty class should I specify for a semi gantry crane?

Start by documenting two things: how many lifts the crane will perform per shift, and what percentage of SWL each lift represents on average. A production line cycling every few minutes at 70–90% SWL needs A5 or higher; a maintenance crane lifting occasionally at varied loads is typically A4. The BMH is rated A4 standard; the BMG covers A5–A7. Specifying too low a duty class is the most common cause of premature component failure.

Q4：Can a semi gantry crane be installed under an existing overhead crane?

Yes — this is one of the most effective capacity upgrades for facilities already running an overhead crane. The semi gantry operates at a lower rail elevation, allowing both units to run in the same bay simultaneously. The key constraint is headroom: the semi gantry girder must clear the existing crane’s lowest hook position by the required structural margin, typically at least 300 mm. Confirm this by measurement before specifying lifting height.

Q5：What certifications should I request when buying a semi gantry crane from China?

For European buyers: a signed EC Declaration of Conformity under Machinery Directive 2006/42/EC, a 125% overload test certificate, and a current ISO 9001 certificate with crane manufacturing in scope. For EAEU markets: EAC certification under TR CU 010/2011. For all markets: structural steel mill certificates and a Factory Acceptance Test report. Request these documents at the enquiry stage — not after manufacturing has begun.